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The Power and Purpose of International LawInsights from the Theory and Practice of Enforcement$

Mary Ellen O'Connell

Print publication date: 2008

Print ISBN-13: 9780195368949

Published to Oxford Scholarship Online: January 2009

DOI: 10.1093/acprof:oso/9780195368949.001.0001

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Unilateral Armed Measures

Unilateral Armed Measures

(p.153) Chapter 4 Unilateral Armed Measures
The Power and Purpose of International Law

Mary Ellen O'Connell

Oxford University Press

Abstract and Keywords

The UN Charter regulates the use of force by states. It permits states to use armed force to enforce a limited set of rights under international law. Principally, states may use force in individual or collective self-defense against a significant armed attack. Even in such a case, force may only be used against the state responsible for the armed attack and only to the extent necessary and proportional to the goal of defense. These rules limit the use of major military force to respond to terrorism. The coalition liberation of Kuwait in 1991 is an example of the lawful use of force in self-defense. The coalition use of force against Iraq in 2003 violated the law. International law clearly prohibits uses of force to pre-empt or prevent threats.

Keywords:   UN Charter, self-defense, state responsibility, necessity, proportionality, armed attack, terrorism, pre-emption, prevention

On August 2, 1990, Iraq invaded its neighbor Kuwait, claiming that Kuwait was legally an integral part of Iraq.1 Iraqi troops led by tanks stormed the tiny emirate on the Persian Gulf, killing Kuwaiti men, women, and children, and looting and destroying property of all kinds.2 In the nineteenth century, Iraq may well have had the right to pursue a territorial claim through the use of force. States no longer have such a right. The 1945 United Nations Charter (UN Charter or the Charter) generally prohibits unilateral armed measures even for enforcing legal rights. Today, states may lawfully use force in only a few situations. One is self-defense. Kuwait had the right to use force against Iraq and other states could join Kuwait in collective self-defense. Most states in the world did join the effort to liberate Kuwait, led by the United States (US). Kuwait was independent once again by February 27, 1991.

(p.154) The world's response to Iraq's invasion shows how far international law had evolved from the situation prevailing in 1899 when, at the First Hague Peace Conference, a number of states pledged to try inquiry or arbitration before going to war.3 While some scholars and governments had never given up on natural law restraints, without a treaty like the UN Charter, it was difficult for positivists to accept that there really was law restricting force. Paradoxically, with the UN Charter's clear limits on the use of force, the right to use force for law enforcement was also generally restricted. In most human communities, as the right to use force was gradually taken away from individuals, it was increasingly concentrated in the hands of public authorities for the purpose of law enforcement. The international community does not have comparable public authorities to those of national and local communities. The United Nations Security Council has primary responsibility to ensure peace and security in the world, but it is not a general law enforcer. The lack of a centralized institution for law enforcement has often been cited as one of the great deficits in international law and one of the reasons why it is dismissed by some from the realm of law.4

Yet, to the extent that international law relies less on force, it might be considered superior to national systems. It is not immediately evident, however, that international law relies less on force than other legal systems. Although the international system does not have a regular police force, states have retained the right to use force in a number of areas, resulting in a system that does not look significantly different from national systems. States may use force in self-defense and in police actions involving low-level force. States acting collectively with Security Council authorization may use force to respond to threats to the peace, in addition to breaches of the peace and acts of aggression. International law subjects every use of force to strict limits, especially through the principles of necessity and proportionality. Thus, the use of force for the enforcement of international law has much in common with the authorized use of force for enforcement in national systems. The armed measures permissible in international law that come closest to domestic police actions are those undertaken by organizations such as the UN, the African Union, or the North Atlantic (p.155) Treaty Organization (NATO). This type of collective armed action will be discussed in Chapter Five, “Collective Armed Measures.” States using low-level force, such as in the arrest of pirate ships on the high seas, are using measures that fall below the type of force regulated by the UN Charter. This type of force will be discussed in Chapter Six, “Unilateral Countermeasures,” and Chapter Seven, “Collective Countermeasures.” This chapter will look at the major category of lawful unilateral armed measures, the use of force in self-defense.

The chapter begins with a brief history of how the use of force came to be generally prohibited in the UN Charter, even for the enforcement of legal rights. It then looks at the general prohibition on the use of force before focusing on the Charter exception for the use of force in self-defense. Although some doubt that self-defense should be considered an example of law enforcement,5 in the international law world, it is arguably appropriate to do so, if for no other reason than the link between self-defense and the historic right to use war and reprisals to enforce international law. More will be said on this issue throughout the chapter.

I. Bringing Force under Positive Law

As described in Part I, “Enforcement Theory,” the legal theories of positivism and absolute sovereignty came to dominate nineteenth-century thinking. When resorting to force, states continued to proclaim the justice of their causes,6 but few apparently held strictly to the Just War Doctrine:

In the science of international law, the nineteenth century was the great era of positivism. …[T]he conception of the law of nature and the kindred one of just war were to all intents and purposes abandoned—the consummation of a process which, as indicated, had started in the eighteenth century.7

The positive law relative to the use of force grew, however. The Paris Declaration on Maritime Law of 1856 (the Paris Declaration) had provisions regulating the conduct of maritime warfare, including the outlawing (p.156) of privateering.8 The Paris Declaration was followed in 1864 by the first of the Geneva Conventions devoted to humanizing the conduct of land warfare. States also continued to develop detailed rules governing neutrality9 and reprisals.10

Reprisals could be undertaken only in response to a wrong, following a demand for compliance. The law required proportionality between the measures of enforcement and the injury. In line with Emmerich de Vattel, the property of nationals could be attached or retained. It was preferred to treat state property as immune, but it, too, could be attached. In addition to such affirmative measures, states could take “negative” or passive action such as denying rights or refusing to fulfill treaty obligations.

The position that resort to reprisals could be regulated but not war was always illogical. This illogic contrasted with the position of natural law adherents who taught that war, along with all human action, was under the restraint of law. Popular peace movements, sympathetic to the just war position, were active, particularly in the United States (US) and Britain in the nineteenth and early twentieth centuries. From the successful resolution of the Alabama Claims between the US and Britain, until the first decade of the twentieth century, these popular movements were passionate advocates for the use of arbitration in place of armed force. They weakened the acceptability of unregulated war.11

The 1898 Spanish-American War galvanized these efforts. That war had been a bloody conflict in which Spain lost most of its remaining overseas colonies to the United States. The popular view was that Spanish agents started the war when they sunk a United States naval vessel, the Maine, in the Port of Havana,12 but peace campaigners adhered to the theory that the ship sank due to an accident, which is now believed to (p.157) be correct.13 They believed mechanisms of peaceful settlement could have clarified the true cause of the Maine disaster, avoiding the war. When the Russian Tsar called for a disarmament conference in 1899, members of the peace movement successfully lobbied him to add peaceful settlement to the agenda. The Tsar was interested in pursuing ways to avoid war, not only to gain the benefits of peace, but in the interest of Russian security. Russia was not keeping pace with other world powers in acquiring the new technology of war, and rather than continue to try to compete, Russia saw a limitation on war as the better course. In other words, Russia sought alternatives to wars it feared it could not win.14

During the First Hague Peace Conference, delegates from twenty-six countries drafted a convention defining and setting out rules and procedures for good offices, mediation, inquiry, and arbitration. The British delegation had formally proposed an international court for the settlement of disputes, but they failed to get sufficient support for the idea. The closest the delegates came to creating a court was the Permanent Court of Arbitration (PCA). The PCA provides a list of available arbitrators, a set of arbitration rules, and a small secretariat in The Hague.15 No state is bound to have resort to it. The PCA rules say nothing about enforcement of awards beyond the provision that disputes respecting the execution of an award may be returned to the tribunal.16 Still, the discussions for a real court and the first steps toward one in the form of the PCA inspired the US delegation, as it left The Hague, to resolve to make further efforts toward creating a real court.

The successful use of inquiry in 1906 to resolve the Dogger Bank dispute, which had nearly resulted in a war between Russia and Britain, added to the enthusiasm for methods of peaceful settlement.17 Delegates to the Second Hague Peace Conference in 1907 added more rules for (p.158) inquiry, and the arbitration rules were modified and improved. Elihu Root at the head of the US delegation tried diligently to get agreement on a permanent international court. Again the idea failed, owing largely to German opposition. The delegates in 1907 did agree to the first multilateral treaty outlawing the use of force for a particular class of disputes, collection of contract debts.18

Despite his enthusiasm for courts as an alternative to war, by 1914, Root believed force would be needed against Germany. America's most prominent international lawyer and founder of the American Society of International Law (ASIL) held firmly to the view that the US needed to go to war against Germany to join in common cause with Britain to put a stop to German imperial designs. German intentions had been clear enough for Root at the peace conference. The German government did not share the Anglo-American enthusiasm for third-party settlement.19 One of the Kaiser's representatives, Baron von Stengel, “still taught [in 1909] the incompatibility of sovereignty with compulsory arbitration and criticized the compromise under which Germany had ‘in principle’ agreed to it in the Hague two years earlier.”20 For him, “British pacifism was British imperialism in disguise.”21 Germany's other representative, Philipp Zorn, did support arbitration, pointing out the ability to reject it in any particular case by citing the “national honor” or “vital interest” clauses.22 German legal scholars were generally lukewarm at best about international law methods for promoting peace “or, as [Hans] Kelsen put it, for pacifism over imperialism. …”23 Some German scholars were plainly suspicious of the barriers to war raised by British and American scholars and officials as a means of preventing Germany from acquiring an empire, while preserving that of the British. Britain had used war to conquer extensive colonies and now was happy to declare peace.

(p.159) After Germany was defeated in the First World War, with the decisive assistance of the United States, it was, of course, no longer an obstacle to the further development of peaceful means of settlement. Woodrow Wilson arrived in Paris with an ambitious plan for a world organization to ensure peace and justice. The Covenant of the League of Nations (the Covenant or the Covenant of the League) was adopted on April 28, 1919,24 having grown out of Wilson's and others' proposals prepared before and during the early stages of the Paris Peace Conference. Neither Root nor any of the other Americans long involved in promoting peace through law were part of the American delegation to the conference.25 Root believed strongly that the United States would not approve what emerged as Article 10 of the Covenant—the commitment “to respect and preserve as against external aggression the territorial integrity and existing political independence of all members of the League.”26 This was an open-ended agreement to go to war, whether in the US national interest or not. Root felt Wilson was promoting this and other ideas with his own legacy in mind, as opposed to what would actually work and what the American people could accept. They would not nor should they enter into a standing agreement to use armed force. The US Senate agreed with Root, and America did not join the League.

In addition to Article 10, the Covenant had several other provisions relevant to the eventual outlawing of the use of force and the enforcement of international law. For example, Article 16 also provided for the use of military force in response to unlawful resort to war. It included economic sanctions and expulsion as enforcement measures for violations of the Covenant.27 The League expelled the Soviet Union following its unlawful invasion of Finland in 1939. Presumably, Article 16 could only be invoked for enforcing the Covenant and not general international law. This was (p.160) Kelsen's view.28 Even with its limited scope of application, however, Article 16 proved too harsh a response for many types of violations. The League did not wish to expel a member for the mere nonpayment of dues, for example.

Article 12 of the Covenant provided for a general restriction on the automatic right to resort to war:

The Members of the League agree that, if there should arise between them any dispute likely to lead to a rupture they will submit the matter either to arbitration or judicial settlement or to inquiry by the Council, and they agree in no case to resort to war until three months after the award by the arbitrators or the judicial decision, or the report by the Council.

Article 13 prohibited resort to war against any state that complied with a judicial or arbitral award or a report of the Council of the League.

These and other Covenant provisions against war were popular in the United States. When the Senate refused to ratify the Versailles Treaty, American leaders nevertheless wanted to show themselves to be on the side of peace. The US Secretary of State, Frank Kellogg, joined with his French counterpart, Briand, to promote a general prohibition on the use of force—something even beyond the Covenant of the League, which only called for delay and attempts at peaceful settlement. Parties to the Kellogg-Briand Pact of 192829 (the Pact) renounced war as an instrument of national policy and committed themselves to seeking the peaceful settlement of disputes. The Pact did not, however, eliminate the right to use force in self-defense, nor was it clear that the Pact was meant to prohibit the use of force for the enforcement of legal rights.30 In addition to the Covenant and the Pact, a number of other bilateral and regional agreements (p.161) for the renunciation of war were adopted in this period.31 A number of constitutions also placed limits on war.32 Even in these cases, however, many governments understood that they retained the right to use force in self-defense or to enforce legal rights.

Among those scholars who believed the Kellogg-Briand Pact and the Covenant prohibited resort to war to enforce legal rights, there were mixed views on whether resort to armed reprisals was prohibited.33 Armed reprisals continued to be used for various purposes, principally enforcing rights. A case that arose before the adoption of the Covenant, but that was decided years after, gave the impression that armed reprisals to enforce legal rights continued to be a lawful form of enforcement, when strict procedures were followed, even after the positive law developments prohibiting war. In the Naulilaa case of 1928, two German military officers and a government official crossed from German South West Africa (today Namibia) into Portuguese Angola in 1914 to discuss food shipments. Due to a misunderstanding caused by poor interpretation, a Portuguese officer grabbed the reins of a German officer's horse. The German officer struck the Portuguese, and one of the German officers drew a pistol at the same time. The Portuguese officer in charge ordered his men to shoot the Germans. All three were killed.

Without discussing the incident with Portuguese authorities, German troops destroyed several Angolan posts in retaliation. After World War I, the Portuguese instituted an arbitration against Germany, in which it was held,

[r]eprisals are an act of self-help (Selbsthilfehandlung) on the part of the injured state, an act corresponding after an unsatisfied demand to an act contrary to the law of nations on the part of the offending state. They have the effect of momentarily suspending, in the relations between the two states, the observance of such or such a rule of the law of nations. They are limited by the experiences of humanity and the rules of good faith applicable in relations between state (p.162) and state. They would be illegal if a preliminary act contrary to the law of nations had not furnished a reason for them.34

Despite the limits on war, if the legal requirements for taking reprisals were met, many considered them a lawful use of armed force to enforce rights. Nevertheless, Ian Brownlie points out that, after the adoption of the Kellogg-Briand Pact in the same year as the Naulilaa arbitration, the use of armed reprisals practically ended.35

Tragically for the world, the use of war did not come to an end. Adolf Hitler, convinced of Germany's superiority, of its natural right to be the dominant power in Europe, gained control of neighbors, then invaded Poland in 1939. Japan's leaders had a similar conviction of superiority and a similar determination to rule over or eliminate peoples they considered inferior. Both aggressor states used sophisticated legal arguments based on self-defense to justify their violations of the law against war. The Second World War finally shocked humanity into taking the next step toward outlawing the use of force. In addition to a general, normative prohibition on the use of force as found in the Kellogg-Briand Pact, the victorious states also agreed to a powerful body to enforce the prohibition: the United Nations Security Council.

II. Prohibiting Force in the UN Charter

American President Franklin Delano Roosevelt's Cabinet began exploring a new design for a world organization to replace the League of Nations as early as 1939.36 What emerged in 1945 at the San Francisco Conference was, in many ways, based on the Covenant and Kellogg-Briand Pact but with important differences. The use of armed force was finally prohibited for all states in UN Charter Article 2(4):

All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or (p.163) political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations.37

Article 2(4) goes farther than either the Covenant or the Pact in that it more obviously excludes the right to use armed force even to enforce most legal rights.38 Under the Charter, states may only lawfully use force to react in self-defense to an unlawful armed attack. Even then, force in self-defense is permitted only until the Security Council acts.39 The Security Council received broader authority than states to act in response to threats to the peace, breaches of the peace, and acts of aggression, and the drafters gave World War II's victorious Allies the right to veto any resolution mandating action.40

Article 2(4) on its face may appear to be very broad indeed in that it refers only to “force,”41 and not to “armed force.” It could reasonably be interpreted to prohibit economic coercion,42 political coercion,43 physical force not involving arms,44 or computer attacks.45 It is clear from the drafting (p.164) history of the Charter, however, as well as the subsequent interpretation and practice by governments and organizations, that the "force" being regulated in Article 2(4) is armed force.46 Other forms of force are outside the scope of Article 2(4).47 These are typically regulated under the principle of nonintervention and not the Charter rules governing the use of force. Coercive measures less than armed force will be considered in the chapters on countermeasures.

It is also by now well established that Article 2(4) prohibits the use of armed force generally, not just uses aimed at the territorial integrity and political independence of states. In the decades since the adoption of the Charter, international lawyers have discussed at length whether the terms territorial integrity and political independence and Purposes of the Organization have any restricting effect on the prohibition of 2(4). By now the weight of opinion, backed by the travaux préparatoires of the Charter and the subsequent legal positions of governments and the International Court of Justice (ICJ), is that 2(4) is a general prohibition on force.48 Article 2(4) plainly bans any use of force by states except those in self-defense and those of a very limited or de minimis nature.

A member of the US delegation at San Francisco stated that “the intention of the authors of the original text was to state in the broadest terms an absolute all-inclusive prohibition; the phrase ‘or in any other manner’ was designed to insure that there should be no loopholes.”49 The final structure of the Charter that emerged in San Francisco underscores the broad scope of Article 2(4). The Security Council was given explicit, broad authority to use force in Articles 39 and 42 against threats to the peace, breaches of the peace, and acts of aggression. By contrast, states acting without Security Council authority receive only a narrow, explicit right to do so in Article 51. Article 51 permits force in individual and collective self-defense “if an armed attack occurs,” and only until such time as the Security Council takes action. Thus, if Article 2(4) only prohibited force aimed at territorial integrity and political independence, Article 51 would be redundant, since defending against an unlawful attack (p.165) would not interfere with the attacking state's territorial integrity or political independence.

Latin American delegates to the San Francisco Conference particularly wanted Article 51 included—something of a last-minute effort. They were concerned that the Rio Treaty arrangements already in existence for collective self-defense would be eliminated by Article 2(4). To clarify that Article 2(4) did not prohibit either the right of individual or collective self-defense, the delegates added Article 51. It is a limited exception to Article 2(4) allowing self-defense in a situation in which it can be shown by the tangible evidence of an armed attack that a state may respond. The response must be limited to defense and may last only until the Security Council acts or the defense is achieved.

To ensure respect for the prohibition, the Security Council was instituted with broader authority to use force than is allowed to states. The Security Council may respond to “threats to the peace, breaches of the peace and acts of aggression.”50 The Charter drafters also provided for the Security Council to have military forces available to be able to respond to threats and breaches. Member states were to contribute these forces under agreements with the Security Council.51

This scheme had real advantages over the Kellogg-Briand Pact and the Covenant: Weaker states would in theory receive help from the Security Council and the Council could act as an objective decision-maker. The Pact had no enforcement system at all—it was a basic prohibition and nothing more. If one state invaded another, the victim state could defend itself and could call on its friends for help, but that was all. The Council of the League of Nations had been intended to help victims, but it had to act through unanimity and was unable to respond to the major challenges. The Security Council, by contrast, was organized as a standing body with clear responsibility to act on behalf of all victim states. Under Article 27(3) of the Charter decisions for enforcement action require nine affirmative votes and no negative votes of the five permanent members—in other words, less than unanimity. And, as mentioned, the Council was to have troops available with which to act. It could also call on regional agencies to act on its behalf. Those regional organizations were otherwise restricted by the Charter in using force to the same degree as states generally. Thus, the (p.166) Council was to be a uniquely powerful organization in the area of peace and security.

The Security Council's power was, however, restricted to the area of peace and security. The UN Charter did not make the Council the general enforcer of the law, just the enforcer of the peace. The delegates debated at San Francisco whether to give the Council general enforcement authority, but decided against it. The leaders gathered at San Francisco were focused on ensuring peace, not instituting a true world police force. “The United Nations Charter accords priority to the peaceful resolution of disputes rather than to the enforcement of law. This was intended by the major powers when the Charter was drafted….”52 The UN Charter does give the Security Council explicit authority to enforce judgments of the International Court of Justice, but the Council has discretion to do so. The League of Nations Council was mandated to enforce judgments of the ICJ's predecessor, the Permanent Court of International Justice (PCIJ), as well as arbitral awards. The Security Council can decide against enforcement of ICJ judgments in the interest of peace. Nor does the Security Council have any role in enforcing arbitral awards.53

So, while the horrors of the Second World War induced some legal development beyond the Covenant of the League in the area of peace and security, the law and means of enforcing international law may not have been advanced. In fact, something of an anomaly developed in the area of international law enforcement. States generally lost the right to use armed force to enforce legal rights except in responding to an unlawful armed attack. In the case of unlawful attack or threat, states could also turn to the Security Council for assistance, but not in the case of other law violations. As Kelsen characterized it, war could still be used to enforce the law—but only the law of the UN Charter.54 For other law violations, the Charter mandates that peaceful means be found.

At various times, since the adoption of the UN Charter, some scholars have taken stock of the state of international relations and have concluded that there are, in reality, no rules restricting the use of armed force. One of the best known of these challenges came in 1970, twenty-five years after (p.167) the adoption of the UN Charter when Thomas Franck wrote that the Charter's core provision—Article 2(4)'s prohibition on the use of armed force—was dead.55 He pointed to indisputable facts: The Security Council was not functioning as intended to enforce the prohibition on force; in the resulting vacuum, states were abusing that article's exceptions; states were claiming to act in self-defense or collective self-defense when they were not; and states were invoking the right of regional organizations to act when they had no foundation for doing so. Franck concluded that the idea of a broad, tough ban on the use of force could not work as long as the institution expected to enforce the ban was dysfunctional and as long as states were so flawed as to be unable to restrain themselves from the unlawful use of force.56

Despite proclaiming the rules dead, Franck could not go so far as to argue the world had reverted to a condition in which there was no prohibition on the use of force. Rather, he described the world emerging from the “ashes of Article 2(4)” as a “world of peacefully co-existing, super-Power-dominated regional spheres.… a world in which the threat or use of violence by super-Powers within their own spheres will largely displace the threat or use of violence among super-Powers.”57

In replying to Franck, Louis Henkin did not dispute that armed force in violation of the UN Charter had occurred in Cuba, Czechoslovakia, the Dominican Republic, Hungary, and possibly Vietnam. He looked intensely at these actual uses of force and saw actual violations but also no interest in abandoning the norm prohibiting force. In the words of Henkin, “The occasions and the causes of war remain. What has become obsolete is the notion that nations are as free to indulge it as ever and the death of that notion is accepted in the Charter.”58 Henkin's prescription for the future was to acknowledge state interest in the norm and to build from there. He rejected Franck's advocacy of a different normative order.

(p.168) Henkin's view was vindicated by the International Court of Justice in 1986 when the Court held that the United States had violated fundamental law in using force against Nicaragua in the absence of an armed attack by Nicaragua. The court held that despite other unlawful uses of force following the adoption of the Charter, the prohibition on force was, indeed, still good law. Article 2(4) had moved beyond treaty law to customary law, and, the court implied, to a jus cogens norm. The court explained that a rule remained viable despite violations depending on whether the community still manifested acceptance of the rule.

If a State acts in a way prima facie incompatible with a recognized rule, but defends its conduct by appealing to exceptions or justifications contained within the rule itself, then whether or not the State's conduct is in fact justifiable on that basis, the significance of that attitude is to confirm rather than to weaken the rule.59

Nevertheless, in 2002, the rules were declared dead again, this time by Michael Glennon:

[S]ince 1945, dozens of member states have engaged in well over 100 inter-state conflicts that have killed millions of people. This record of violation is legally significant. The international legal system is voluntary and states are bound only by rules to which they consent. A treaty can lose its binding effect if a sufficient number of parties engage in conduct that is at odds with the constraints of the treaty. The consent of United Nations member states to the general prohibition against the use of force, as expressed in the Charter, has in this way been supplanted by a changed intent as expressed in deeds.… It seems the Charter has, tragically, gone the way of the 1928 Kellogg-Briand Pact which purported to outlaw war and was signed by every major belligerent in World War II.60

(p.169) Glennon's position fails to consider the argument of Henkin, the ICJ, and now Christine Gray, who argues that “some of these writers [such as Glennon] also discount what the states using force actually say in justification of their use of force.”61 In particular, “they ignore the fact that states generally do not claim revolutionary new rights to use force, but try to defend their use of force by claiming self-defence or other legal justifications.”62

Official positions of states and organizations are what make positive law. Official support for a rule against armed force, even when the rule is being violated, does indeed reinforce the rule. States employing armed force in violation of Article 2(4) have not claimed that Article 2(4) does not exist or is not binding, but rather have attempted to validate their behavior by claiming that they are actually acting in compliance with Article 2(4) and the exceptions for self-defense or invitation.

In the decades since the adoption of the UN Charter, as the critics have rightly pointed out, states have engaged regularly in the unlawful use of force. These uses of force and the reactions to them encompass practice that can impact the content of legal rules. Practice that reflects the legal position of states and organizations can modify a treaty rule, eliminate it, or solidify it.63 In fact, some provisions of the UN Charter have been effectively modified through practice.64 Yet, the international community has typically taken a restrictive, rather than a permissive, position with regard to rules on the use of force.65 Decisions of the ICJ and other courts and tribunals have continued to underscore the vitality of the UN Charter.66 This was seen dramatically in 2005 when states at the United Nations World Summit gave overwhelming support to the Charter of 1945.67

(p.170) III. Defending Rights with Force

The most important exception to the UN Charter's prohibition on force for states acting unilaterally is self-defense. Charter Article 51 “licenses at least one kind of resort to armed force by an individual member State: namely, the use of armed force to repel an armed attack.”68 Article 51 provides that:

Nothing in the present Charter shall impair the inherent right of individual or collective self-defense if an armed attack occurs against a member of the United Nations, until the Security Council has taken the measures necessary to maintain international peace and security.69

The UN Charter permits the use of armed force, according to Stanimir Alexandrov, “to protect the security of a State and its essential rights, in particular the rights of territorial integrity and political independence. Self-defense does not include a right to exact reparation for injury.”70

Alexandrov uses terms that fit the law enforcement paradigm—a state may use force to protect essential rights. Josef Kunz, however, objected to characterizing the use of force in self-defense as an aspect of law enforcement. He did not classify the use of force in responding to an attack as a sanction but rather self-protection. It is true that, in domestic law, we do not typically categorize self-defense as a legal sanction. Yet, Kelsen certainly included self-defense as a prime example of a justifiable use of force under the Just War Doctrine.71 Kunz's objection seems to be that self-defense is a form of self-help and self-help is not a true legal sanction. From his perspective, international law today has few legal sanctions, since international law sanctions continue to be characterized largely by self-help, but, if the law prescribes them, they are, arguably, legal sanctions.

David Luban of Georgetown University has also said that force in self-defense is not always force for law enforcement.72 He points to Iraq's unlawful 1990 invasion of Kuwait saying Iraq could defend itself (p.171) when counter-attacked. In fact, while Iraq's soldiers could lawfully defend themselves, the state of Iraq had the legal obligation to withdraw from Kuwait without further fighting.73

Luban accepts that the use of force by third parties in collective self-defense is law enforcement. Third parties assisting a victim state are evidently not resorting to self-help. Yet, the only legal justification for resort to force in collective self-defense is that a state has been unlawfully attacked—the same basis on which the victim itself has the right to act. The collective action is no more authorized in international law than the individual action—indeed it is less authorized in that third parties must have a request for assistance from the victim. The victim may choose to defend alone or not defend at all. Collective action has the virtue of greater objectivity, as Hugo Grotius pointed out, but collective action in self-defense is not the substitute in international law for authorized police action. The closest international law has to police action is through the Security Council. States joining in collective self-defense without Security Council authorization are acting lawfully but on the same legal basis as the victim. If the action by the group is law enforcement so is the action by the victim. Admittedly, there is room for disagreement on these points, but the position taken in this chapter is that the use of force in individual as well as collective self-defense may be categorized as law enforcement in international law against unlawful armed attack.

The rules on self-defense today include the reaffirmed UN Charter provisions and several important general principles of international law. In brief, a state may use significant force on the territory of another state when four conditions are met:

  1. 1. A significant actual armed attack has occurred or is occurring;

  2. 2. The response in self-defense is aimed at the armed attacker or those legally responsible for the attack;

  3. 3. The response is necessary to defense;

  4. 4. The reponse is proportional in the circumstances.74

(p.172) Self-defense is a term of art in international law. The reference to self-defense in Article 51 is to the right of the victim state to use significant offensive military force on the territory of a state legally responsible for the attack for the purpose of defense.75 The defending state may do more than stop an ongoing attack. It may assure its future security by degrading the attacker's offensive military capability or temporarily holding territory. Necessity and proportionality still limit what the defender may do but the limits are apparently not as strict as in the case of a de minimis use of force to effect an arrest. Necessity and proportionality in the case of self-defense are discussed further below. The point here is that the triggering events to self-defense occur at a high level because the response in self-defense may permissibly involve significant armed force.76

Armed Attack

The clearest restriction on the lawful use of force in self-defense is Article 51's requirement that an armed attack occur before resort to force. This requirement is stated in plain terms in Article 51. It creates a requirement open to objective testing, so it has been particularly difficult for states to argue that they need not comply with it. The French version of the UN Charter indicates an even higher threshold—not just armed attack but aggression armée (armed aggression—more than a single attack) triggers the right. Nevertheless, arguments have been made to ignore the plain terms, to interpret them broadly, or to privilege the term inherent in the phrase “inherent right of self-defense” over the phrase “if an armed attack occurs.” As the review of relevant practice below will reveal, such arguments have generally proved less persuasive than the importance of a clear, objective rule that can work in a legal system still based largely on self-policing.

On one point, those who favor restricting force as much as possible have probably not prevailed. Most scholars reject extending the requirement of armed attack to a need for a state to actually absorb the first blow. Article 51 in the English version requires that an armed attack “occurs,” not (p.173) that it has already “occurred.” Sir Humphrey Waldock wrote in 1952 that “[w]here there is convincing evidence not merely of threats and potential danger but of an attack being actually mounted, then an armed attack may be said to have begun to occur, though it has not passed the frontier.”77 Note, however, that Waldock's formula fits the English Article 51 because “if armed attack occurs” can mean “if an armed attack is occurring.”

Proponents of a broader right of anticipatory self-defense generally base their arguments on the word inherent in Article 51.78 The argument is that Article 51, by pledging not to “impair the inherent right of self-defense,” left intact and unchanged the law of customary self-defense predating the adoption of the UN Charter. Henkin relates that this theory emerged during the Suez Crisis to justify using force against Egypt after Gamal Abdal Nasser nationalized the Suez Canal.79 The use of force in that situation was widely condemned, including by the Eisenhower administration.80 Still, versions of the argument persist that the customary law predating the UN Charter allowed the use of force in self-defense, even absent an armed attack. A more conservative version holds that customary international law permitted anticipatory self-defense when an attack was imminent.81

The inherent right theory has numerous weaknesses, starting with its reliance on customary international law before the adoption of the UN Charter. Scholars who advocate the inherent right theory often cite the 1842 correspondence between the United States and Britain over the scuttling of the ship Caroline in 1837 by British forces over Niagara Falls.82 They cite the incident for the proposition that a state facing an imminent threat may use force, even before any armed attack is underway. US Secretary Webster wrote to Lord Ashburton: (p.174)

The President sees with pleasure that your Lordship fully admits those great principles of public law, applicable to cases of this kind, which this Government has expressed; and that on your part, as on ours, respect for the inviolable character of the territory of independent states is the most essential foundation of civilization. And while it is admitted on both sides that there are exceptions to this rule, he is gratified to find that your Lordship admits that such exceptions must come within the limitations stated and the terms used in a former communication from this Department to the British plenipotentiary here. Undoubtedly it is just, that while it is admitted that exceptions growing out of the great law of self-defence do exist, those exceptions should be confined to cases in which the “necessity of that self-defence is instant, overwhelming, and leaving no choice of means, and no moment for deliberation.”83

At the time of the correspondence there was no UN Charter, of course, and so it is difficult to understand how the incident can be used to eliminate Article 51's armed attack requirement.84 The UN Charter was adopted for the very purpose of creating a far wider prohibition on force than existed under treaty or custom in 1945, let alone 1842. Even if earlier custom allowed preemptive self-defense, to argue that it persisted after 1945 for UN members, requires privileging the word inherent over the plain terms of Article 2(4) and the words armed attack in Article 51. Indeed, it requires privileging one word over the whole structure and purpose of the UN Charter. The drafters specifically designed the Security Council to meet threats to the peace, preserving the right of a state to act unilaterally only in cases of armed attack. In cases lacking the objective evidence of an armed attack, the UN Charter requires multilateral decision-making by the Security Council. Permitting preemptive self-defense at the sole discretion of a state is fundamentally at odds with the Charter's design. It is an exception that would overthrow the prohibition on the use of force in Article 2(4) and thus the very purpose of the UN.

(p.175) Some writers promoting the inherent right theory argue that the parameters of the right of self-defense are unchangeable by UN Charter text and subsequent state practice. International law has unchangeable norms—the jus cogens principles. But no court has ever identified a unilateral right of anticipatory self-defense as a jus cogens principle. The UN Charter's drafters intended that states would rely on the Security Council to deal with concerns about international security. Indeed, the ICJ has indicated that the UN Charter prohibition on the use of force, Article 2(4) is jus cogens, not self-defense.85 In the words of Henkin, the inherent right theory is “unfounded, its reasoning is fallacious, its doctrine pernicious.”86

The benefit of waiting until an attack actually occurs is that there is little risk of mistake. Dinstein has written that Israel may have made a good faith mistake in 1967 when it attacked Egypt.87 Israel stated on both June 5 and June 6 that it acted in self-defense against actual air and armored attacks on the territory of Israel.88 Soon after, it represented that it had had convincing intelligence that Egypt was about to attack—that preparations were under way. This was apparently not the case.89 Responsibility for such a mistake is a debated point in international law. Some writers suggest that if the state taking enforcement measures made a good faith mistake regarding the gravity of the violation, the disproportionate response based on that mistake should be excused. Others believe international law is a strict liability system. States are responsible if the results of their actions violate the law. Strict liability has the advantage of acting as a restraint on coercive action. Yet, in the many examples in which force was used based on a mistaken belief, international reaction has tended to accept apology and compensation as sufficient redress. Charges of aggression or violation (p.176) of Article 2(4) are only rarely made in these cases. Still, the 1967 Arab-Israeli War is not a unproblematic example of anticipatory self-defense.

The ICJ, in a case brought by Nicaragua against the United States in 1986,90 concluded that UN Charter Articles 2(4) and 51 had become part of customary international law given that they were so widely accepted as binding law by the time of the case.91 The ICJ further found that Articles 2(4) and 51 prohibit the use of force except in self-defense against acts amounting to a significant armed attack. The United States had maintained at the preliminary stages of the case that Nicaragua had attacked El Salvador by supplying weapons to rebels fighting El Salvador's government. The US joined in collective self-defense with El Salvador in defending against these shipments, which the US characterized as constituting armed attack. The ICJ found, however, that the low-level shipments of weapons from Nicaragua to the El Salvador did not amount to an armed attack which could trigger the right of self-defense:

[A]n armed attack must be understood as including not merely action by regular armed forces across an international border, but also “the sending by or on behalf of a State of armed bands, groups, irregular or mercenaries, which carry out acts of armed force against another State of such gravity as to amount to” (inter alia) an actual armed attack conducted by regular forces.… The Court sees no reason to deny that, in customary law, the prohibition of armed attacks may apply to the sending by a State of armed bands to the territory of another State, if such an operation, because of its scale and effects, would have been classified as an armed attack rather than as a mere frontier incident had it been carried out by regular armed forces. But the Court does not believe that the concept of “armed attack” includes not only acts by armed bands where such acts occur on a significant scale but also assistance to rebels in the form of the provision of weapons or logistical or other support. Such assistance may be regarded as (p.177) a threat or use of force, or amount to intervention in the internal or external affairs other States.92

Later in the decision, the ICJ stated affirmatively that it was unable to consider “provision of arms to the opposition in another State constitutes an armed attack on that State.”93

The ICJ's reference to the sending of armed bands is from the General Assembly's Definition of Aggression.94 The definition lists other acts that trigger the right of self-defense, when, as the ICJ emphasized, the act is on a significant scale. Such acts include invasion of territory, bombardment of territory, blockade of ports, attack on air, sea or land forces, and the “sending … of armed bands, groups, irregulars or mercenaries, which carry out acts of armed force against another State of such gravity as to amount to the acts listed above, or its substantial involvement therein.”95 Self-defense may include similar acts.

The ICJ in the Nicaragua Case confirmed that, under international law, states may only use force to respond to a provocation amounting to an armed attack. Core principles on the use of force enunciated in the Nicaragua Case were reconfirmed by the ICJ in the Oil Platforms Case, and the Congo Case. The Ethiopia-Eritrea Claims Commission also underscored the importance of restricting self-defense to cases of significant armed attack.96 As the ICJ said in Oil Platforms:

[I]n order to establish that it was legally justified in attacking the Iranian platforms in exercise of the right of individual self-defence, the United States has to show that attacks had been made upon it for which Iran was responsible; and that those attacks were of such a nature as to be qualified as “armed attacks” within the meaning of that expression in Article 51 of the United Nations Charter, and as understood in customary law on the use of force. As the Court observed in the case concerning Military and Paramilitary Activities in and against (p.178) Nicaragua, it is necessary to distinguish “the most grave forms of the use of force (those constituting an armed attack) from other less grave forms.” (I.C.J. Reports 1986, p. 101, para. 191), since “In the case of individual self-defence, the exercise of this right is subject to the State concerned having been the victim of an armed attack” (ibid., p. 103, para. 195).97

In June 2002, US President George W. Bush in a speech at the West Point Military Academy, indicated “that not only will the United States impose pre-emptive, unilateral military force when and where it chooses, but the nation will also punish those who engage in terror and aggression and will work to impose a universal moral clarity between good and evil.”98 Similar statements appeared subsequently in several official documents—the Secretary of Defense's first Annual Report to the President and the Congress,99 issued in August 2002, and the White House's National Security Strategy of the United States of America, released in September 2002.100 The 2006 National Security Strategy also stated a claim for the right to use force to pre-empt future attacks.101 Arguments supporting the use of preemptive force as outlined in these documents basically indicate that it is dangerous to wait for evidence that an armed attack is occurring. The use of nuclear, chemical, and biological weapons can be devastating and such weapons, in the hands of an enemy, are evidence enough that a state has the right to use force in self-defense.102 Yet the drafters of the UN Charter were familiar with arguments that force had to be used before danger could grow. Hitler had used the argument to justify the invasions of Norway and the Low Countries. The UN Charter's scheme intends that states in fear of a (p.179) future armed attack should bring their concerns to the Security Council, which may then take action should it find a threat to international peace.

What Henkin wrote in 1987, remains compelling twenty years later:

It is not in the interest of the United States to reconstrue the law of the Charter so as to dilute and confuse its normative prohibitions. In our decentralized international political system with primitive institutions and underdeveloped law enforcement machinery, it is important that Charter norms—which go to the heart of international order and implicate war and peace in the nuclear age—be clear, sharp, and comprehensive; as independent as possible of judgments of degree and of issues of fact; as invulnerable as can be to self-serving interpretations and to temptations to conceal, distort, or mischaracterize events. Extending the meaning of “armed attack” and of “self-defense,” multiplying exceptions to the prohibition on the use of force and the occasions that would permit military intervention, would undermine the law of the Charter and the international order established in the wake of world war.103

When Henkin wrote these words, he was responding to arguments generated by Reagan administration officials that the United States would be safer if it used military force to replace communist regimes with democratic ones. Within a year of that argument, people living under communism were replacing their own regimes and with arguably far better results than if attempts had been made to do so militarily.

Despite these results, similar arguments developed over the course of the 1990s that authoritarian regimes should be opposed militarily to support human rights, including the right to democracy. These arguments drew upon the earlier anticommunist and prohumanitarian intervention arguments originating in the 1970s. Richard Lillich was an early proponent of military force to enforce human rights as a matter of moral imperative.104 He argued that the UN Charter promotes both peace and human rights, and that we should not give priority to the peace rules over the (p.180) human rights rules by limiting the enforcement power of states. He further argued that practice under the UN Charter had modified the Charter, even though its plain words did not permit the unilateral use of force absent an armed attack. He cited the Indian invasion of West Pakistan as an example;105 the Tanzanian invasion of Uganda and Vietnam's Cambodian incursion are two other common examples. In fact, neither Vietnam nor Tanzania justified their actions as humanitarian. To the extent India did, its intervention was internationally condemned.106 Gray shows that until NATO's 1999 military intervention in the Kosovo crisis, states simply did not justify uses of force on the basis of humanitarian intervention.107 Rather, they took the position, time and again, that force could not be used for such purposes without Security Council authorization.

In 1999, NATO bombed Yugoslavia for seventy-eight days to force the Yugoslav leader Slobodan Milosevic to pull the country's forces out of the province of Kosovo and away from the ethnic Albanian population. He finally did, under pressure from the Russians, who pointed out that NATO could bomb indefinitely. The deaths and devastation caused by the bombing and the terrible aftermath, during which Serbs and UN Peacekeepers were killed, may have slowed the development of a new right to use force without Security Council authorization.

The people who drafted the UN Charter in the wake of World War II had a much clearer understanding of the nature of war, as well as what it can accomplish and what it cannot. The UN Charter prohibition on humanitarian intervention has well-considered moral and pragmatic underpinnings. For that reason, it has withstood the arguments in favor of such intervention. There are two primary factors that support the prohibition on humanitarian intervention: (1) the severe pragmatic difficulty of protecting human rights through war, and (2) the weakening of the legal regime for peace—and international law generally—that result from disrespect for the UN Charter prohibition. The UN Secretary General's High Level Panel on United Nations Reform in November 2004 reaffirmed the prohibition on the use of force without Security Council authorization (p.181) except in self-defense.108 At the 2005 UN World Summit in New York, it was reconfirmed that states do not have the unilateral right to intervene for humanitarian purposes.109 There must be an armed attack to trigger the right to respond with armed force.

State Responsibility

Beyond the core requirement of an armed attack, international law places several other conditions on the right to use force in self-defense. These conditions are found in general international law, rather than the explicit terms of Article 51. For example, it is a general principle of law that a state using force in self-defense must target the party responsible for the unlawful attack giving rise to the right of self-defense. If the defense is to be carried out on the territory of a state, that state must be legally responsible for the attack that triggered the defense or be unable or unwilling to prevent future attacks. A state will also be responsible if it sends its own agents to carry out an attack, orders others to do so, or controls a group that carries out an attack.110

In 1999, in the Tadić Case, the International Criminal Tribunal for the Former Yugoslavia found that the

[c]ontrol required by international law may be deemed to exist when a State (or, in the context of an armed conflict, the Party to the conflict) has a role in organising, coordinating or (p.182) planning the military actions of the military group, in addition to financing, training and equipping or providing operational support to that group.111

Under this test, the links between the Taliban and al Qaeda, for example, might have been sufficient to support the US use of force in self-defense against Afghanistan in 2001. The ICJ, however, in three decisions, two since Tadić, imposed a higher test for responsibility. The ICJ ruled in the Nicaragua case in 1986,112 the Congo case in 2005, and the Genocide Convention case in 2007, that a state must be in control of a nonstate actor group for the state to bear legal responsibility and be the legitimate target of the use of force in self-defense.113 This may mean that the links between al-Qaeda and the Taliban were too weak to justify using force in self-defense against Afghanistan. Nonetheless, the Taliban's refusal or inability to eliminate the threat posed to the United States by al Qaeda may have been sufficient to trigger the subsequent military action against al Qaeda in Afghanistan. At any rate, the argument of self-defense was generally accepted.

Terrorist attacks particularly raise the issue of state responsibility. The classic treatment of terrorist acts is to regard them as crimes unless a series of acts amounts to armed attack justifying armed force in self-defense either against a foreign state or against a group within the state. To use force lawfully in self-defense against a foreign state requires a showing that the foreign state is either responsible for the armed attacks of the terrorists or is unable or unwilling to control them. We review below a number of cases in which a state used force claiming self-defense following a clandestine terrorist attack but where the world was uncertain as to the responsibility of the targeted state. These cases all involve force in self-defense, meaning the defending state chose to use significant force on the territory of another state.

The United States was heavily criticized for using force against Libya in 1986. In that year, we now know without doubt from East German (p.183) Ministry for State Security (Stasi) files and other sources, that Libya supported the bombing of a disco in Berlin, where United States servicemen were often present.114 Two US servicemen and a local woman were killed in the incident. The United States had evidence of a plan for more attacks.115 In response, it targeted military sites in Libya. The Libyan head of state, Colonel Ghaddafilived at one of these sites and, tragically, his young daughter was killed.116 Presumably, the United States knew of Ghaddafi's living arrangements, and, thus, one can question whether the US attack was proportional.117 Much of the criticism around the incident may have been generated because of the loss of civilian life, but governments at the time also seemed to doubt the US evidence of Libyan involvement. Part of the concern that persisted for years following the attack was doubt over the US evidence of Libya's involvement, past and future. In 2001, a German court affirmed the US evidence—the bombers were Libyan agents.118 Also, a Libyan agent was convicted in 2001 for the 1988 bombing of an American passenger jet over Lockerbie, Scotland, which resulted in the deaths of 270 passengers and crew.119

In the mid-1990s, following acts of terror in Iran by Kurdish separatists, Iran used force against them on the territory of Iraq. The Iraqi government was unable to control the acts of the Kurds in northern Iraq owing to the fact that since the 1990–1991 Gulf War, the US and UK had kept Iraqi forces out of the north with the establishment of the “Iraqi Exclusion Zone.”120 Iran explained to the Security Council, that “in response to these armed attacks from inside Iraq and in accordance with Article 51 of the Charter of United Nations, the fighter jets of the Islamic Republic Air Force carried out a brief, necessary and proportionate operation against the military bases of the terrorist group where the recent (p.184) armed attacks originated.”121 Similarly, Turkey has pursued Kurdish terrorists into Iraq on several occasions. It explained to the Security Council in 1995 that, “Turkey cannot ask the Government of Iraq to fulfil its obligation, under international law, to prevent the use of its territory for the staging of terrorist acts against Turkey. Under these circumstances, Turkey's resorting to legitimate measures which are imperative to its own security cannot be regarded as a violation of Iraq's sovereignty.”122 The United States has explicitly stated that Turkey was acting in self-defense. It is unclear why Turkey itself did not invoke Article 51.123 The European Union and the Council of Europe criticized Turkey's earlier interventions as disproportionate. Neither body has sanctioned Turkey.124

In 1998, trucks rigged with bombs blew up outside the United States embassies in Nairobi and Dar-es-Salaam. Hundreds died, including twelve Americans, but most were local residents; hundreds more were wounded and blinded, all Africans. The United States determined that a terrorist group under the leadership of a wealthy Saudi named Osama bin Laden was responsible. The US believed bin Laden had ties to a manufacturer in Khartoum and trained terrorists at a remote site in Afghanistan. The US bombed a factory in Khartoum owned by the manufacturer and bombed a camp in Afghanistan. The US evidence respecting the factory and its claim that the factory produced chemical weapons was widely questioned. The raid on the camp in Afghanistan received more support, though the criticism of the Khartoum bombing clouded the US's claims in general.125

On October 7, 2001, the United States and United Kingdom used force in Afghanistan, claiming lawful self-defense. They argued that they had evidence that the September 11, 2001 (9/11) attacks on the World Trade Center in New York and the US Department of Defense headquarters at the Pentagon in Washington were part of a series of terrorist actions against the United States begun with the 1993 attack on the World Trade (p.185) Center, continued with the embassy bombings in Tanzania and Kenya and the attack on the USS Cole in Yemen, and that there would be future attacks. This evidence was presented to members of NATO and was called “compelling.”126 After the use of force against Afghanistan began, the US forces said they found documentary evidence that members of al Qaeda planned further attacks on the United States.127

State reaction to Operation Enduring Freedom in Afghanistan was supportive on the facts and the law at the time. In several subsequent resolutions relating to terrorism and the situation in Afghanistan, neither the Security Council nor the General Assembly condemned Operation Enduring Freedom as a violation of the UN Charter.128 The attacks of 9/11 were seen as armed attacks within the meaning of Article 51. The prior attacks and evidence of intent to carry out future attacks supported the argument that attacking Afghanistan was for the purpose of defense.

As discussed above, however, subsequent decisions of the ICJ indicate that a higher level of control by the Taliban of al Qaeda should have existed to justify holding Afghanistan responsible. The negative consequences of the invasion may also reinforce for governments that the use of force in self-defense should be undertaken only in the clearest case of responsibility. Similar negative consequences followed the 2007 Ethiopian invasion of Somalia. The Ethiopian Prime Minister Meles Zenawi said six months after the invasion that his government

“made a wrong political calculation” when it intervened in Somalia…. Addressing Ethiopia's Parliament, Meles said his government incorrectly assumed that breaking up the Islamic movement that took control of most of Somalia in June 2006 would subdue the country.… Opposition members of Parliament have accused Meles of making the same mistake in Somalia that critics say the Untied States made in Iraq: launching a military intervention without having a political plan. Many Ethiopian intellectuals and political leaders opposed (p.186) the intervention because they said it would inevitably create the conditions for the sort to Somalia-based terrorist attacks that Meles intended to contain by invading the country.129

The United States pressed Ethiopia to invade to push a coalition of conservative Islamic groups out of power.130 It provided intelligence, logistics, and its own commandos.131 The United States linked the Islamic group running Somalia to support for al Qaeda and other Islamic extremists. Following the Ethiopian invasion, however, the situation in Somalia deteriorated, as the Prime Minister of Ethiopia admitted.

Necessity and Proportionality

Results like those following the Ethiopian-U.S. invasion of Somalia point to additional requirements for lawful self-defense: necessity and proportionality. The use of force must be necessary to accomplish the defensive purpose at an acceptable cost. The 2007 Ethiopian intervention in Somalia caused hundreds of deaths, much destruction, and after six months was proving counterproductive to the goal of defense.132

Necessity and proportionality are not expressly mentioned in the UN Charter, but the ICJ held in the Nuclear Weapons Case, “there is a ‘specific rule whereby self-defence would warrant only measures which are proportional to the armed attack and necessary to respond to it, a rule well established in customary international law.’ This dual condition applies equally to Article 51 of the UN Charter, whatever the means of force employed.”133 An armed response in lawful self-defense must be made in a way that conforms to the principles of necessity and proportionality.

Necessity with respect to self-defense means that even armed measures taken in direct response to an armed attack must have a defensive purpose. (p.187) They may not be undertaken if it is clear that the attacker is not going to attack again or if the response is not designed to have a defensive purpose. Armed measures taken in these situations are reprisals, which are unlawful today.134 They are not considered measures of self-defense—they do not repel ongoing armed attack or seek to dislodge an unlawful occupation.

The necessity requirement of responding to ongoing attacks places another limitation on lawfully using significant military force to respond to terrorist attacks. In addition to the state responsibility issue discussed above, terrorists may attack at one place, and then move on to another so that responding in self-defense becomes problematic. This is another reason why terrorism should generally be treated as a crime and not the trigger of armed conflict in self-defense. Still, as discussed above, in some cases if terrorists have conducted a series of significant attacks, planned future ones, and their identities and whereabouts are known to the defending state. the conditions of lawful self-defense may be met, as long as the defense is necessary and proportional.135

Nevertheless, these are rare cases. In reality, it is very difficult to get sufficient evidence of an ongoing terror campaign to support the right to use force in self-defense. The state victim of terrorists may have some evidence of a plan of future attacks but that is not the same as the reality of an ongoing attack. Evidence of plans from secret intelligence sources is far from the self-defense scenario contemplated in the UN Charter—ongoing armed action by a regular military force. In several cases in which states used force in response to terror acts, claiming the right of self-defense, they have been criticized. Generally, the evidence of who actually carried out the attack was weak and the evidence of future attacks, nonexistent. Even in the strongest case of ongoing attack, the response must still be proportional in the circumstances, and the state in which the perpetrators are located must refuse to cooperate in ending the attacks. If those conditions are met, however, a compelling case for self-defense is made.

Israel invaded Lebanon in 1982 in response to attacks by the Palestine Liberation Organization (PLO). The invasion went as far as the capital, Beirut, far from the area where attacks on Israel originated. The Israelis (p.188) remained in Lebanon for three-and-one-half months. The United States believed Israel had a right of self-defense with regard to the attacks it was suffering, but nevertheless also believed that Israel's response was out of proportion to the attacks.136 The 2006 Israeli invasion of Lebanon was criticized on the same basis. Israel had the right to stop rocket attacks into its country launched by Hezbollah fighters. It had the right to attempt to rescue kidnapped Israeli soldiers, but bombing heavily civilian areas far from Hezbollah rocket emplacements was arguably disproportionate.

The amount of force used during the first weeks of the US and British action against Afghanistan in 2001, appeared necessary and proportionate—certainly while the US restrained the Northern Alliance from seizing Kabul. US Secretary of State Powell indicated that the US did not aim to eliminate the Taliban entirely. His approach tracked the international legal rules.137 Degrading the Taliban's offensive ability was a legitimate objective. The care taken in targeting to avoid civilian casualties kept the force used proportionate. Changing the government of Afghanistan was arguably not necessary, however, for the defense of the US. Nevertheless, the Northern Alliance took Kabul. After the Taliban fell in mid December, the continued use of massive aerial bombardment was arguably disproportionate to the objective of capturing small groups and individual al Qaeda members scattered in the Afghan mountains. The shift to ground forces in mid January was more protective of civilians.

The principles of necessity and proportionality apply even though the reason for going to war is unlawful. It is nonetheless difficult to apply them when not measured against a lawful goal. In the case of Iraq 2003, the announced reason for the invasion was to enforce Iraq's disarmament obligations, and, in the US case, apparently pre-emptive self-defense from obtaining weapons of mass destruction. The Australian and British letters to the Security Council both promised to use limited force:

The objective of the action is to secure compliance by Iraq with its disarmament obligations as laid down by the Council. All military action will be limited to the minimum measures (p.189) necessary to secure this objective. Operations will be conducted in accordance with the international laws of armed conflict.138

The previous attempt by the US and Britain to get Iraq to comply with its weapons obligations, Operation Desert Fox of December 1998, failed utterly. Conditions had not changed in the intervening four years to indicate the use of force was any more likely to succeed in March 2003. Thus, using force could not achieve the military objective of getting Iraq's government to disarm. And, in fact, it did not succeed. The government was thrown into disarray with no possibility to then disarm, even if there had been weapons of mass destruction to give up.

Further, given that the objective of disarmament could not succeed through a strategy of massive force, the deaths of any civilians was disproportionate. The utter lack of proportionality between military objectives and civilian deaths was underscored by the fact the coalition had a far less lethal alternative by which to achieve disarmament—the UN weapons inspectors, backed up by economic sanctions.

Finally, the defensive use of force need not necessarily follow immediately from the unlawful armed attack, depending on the circumstances. Some brief time to organize the defense is permissible.139 In the case of Iraq's unlawful use of force against Kuwait in 1991, the Security Council actually required a six-month delay before the defense could begin, to give peaceful measures a chance to work (a time period during which the US-led force to liberate Kuwait mustered troops and equipment). On the other hand, a state which has not taken immediate action should notify the Security Council to ensure that the time for action has not passed. States using force in self-defense must at any rate notify the Security Council under the terms of Article 51. If there is no action by the Council after the notice and the victim delays for a substantial period, it can no longer plead self-defense and must turn to peaceful means to enforce its rights.140 This should be the case whenever a significant period has transpired with no (p.190) active effort towards self-defense. Should a long delay occur, the victim may still have a claim against the wrongdoer, just not a right to use force in self-defense.141 The scheme of the UN Charter is to promote the peaceful settlement of disputes. The right to use armed force is permitted only in situations that may be characterized as emergencies, analogous to the right to use force in personal self-defense. If the emergency passes, other means must be used for enforcing the claim.

For example, the first attack by al Qaeda against the World Trade Center Towers in New York City occurred in 1993. Using force in self-defense might have been lawful but was completely impractical. It took time to discover who the perpetrators were and where they were. When the US did learn about the perpetrators, it extradited a number of persons who stood trial and went to prison. By the time the US made its case against these members of al Qaeda and discovered the links to Afghanistan, it was too late to use military force even if all the requirements of lawful force could be met.

In classical international law, states had the right to resort to war and reprisals to enforce their rights. Under the leadership of the United States, the world established a peace order in 1945 to clearly outlaw the use of force, even for the enforcement of legal rights. A number of exceptions were made to the general prohibition. The Security Council was given the responsibility to maintain peace and security. It could respond to threats to the peace, breaches of the peace, and acts of aggression, including through the use of military force, which it has done by authorizing states to use force as in the liberation of Kuwait in 1990–1991. States acting unilaterally may use force in self-defense if an armed attack occurs, the defense targets the responsible state, the defense is necessary and proportional, the Security Council is notified, and until such time as the Security Council acts. In other cases, international law provides alternative means of enforcement, as will be discussed in the next chapters.

Despite the normative superiority of limiting the right to use force, governments, representatives of organizations, and scholars, have challenged the UN Charter paradigm on the use of force at various times for various reasons. A few have declared the rules dead. Others have tried to expand the right to use force for humanitarian crises, to promote (p.191) communism or democracy or against terrorism, and to enforce other rules of international law. In the aftermath of the Kosovo crisis and the invasions of Afghanistan (2001), Iraq (2003), and Somalia (2007), the UN Charter's clear rules for peace look as compelling as at any time in their history. The time appears right to re-emphasize that the UN Charter's rules on use of force, especially the general prohibition, is not mere positive law, changeable at the at the wish of a national leader. The prohibition in Article 2(4) is a jus cogens norm. The time may also be right to expand the prohibition, to consider an international legal limit on internal armed conflict. (p.192)


(1) For a history of the dispute, see BORDER AND TERRITORIAL DISPUTES 245–47 (Alan J. Day ed., rev. 2d ed. 1987).

(2) R. W. Apple, Invading Iraqis Seize Kuwait and Its Oil; U.S. Condemns Attack, Urges United Action, N.Y. TIMES, Aug. 3, 1990, at A1.

(3) See The Final Act of the Peace Conference, 1899, in 2 JAMES BROWN SCOTT, THE HAGUE PEACE CONFERENCES 1899 AND 1907 61, 83–85 (1909).

(4) “The greatest deficiency, as many see it, is that international society lacks an executive authority with power to enforce the law.” LOUIS HENKIN, HOW NATIONS BEHAVE 24 (2d ed. 1979).

(5) See infra pp. 170–71.

(6) Joachim von Elbe, The Evolution of the Concept of the Just War in International Law, 33 AJIL 665, 685 (1939).


(8) Id. at 192.

(9) WILHELM G. GREWE, THE EPOCHS OF INTERNATIONAL LAW 533–42 (Michael Byers trans., rev. 2000) (The United States was a leading proponent of neutrality law in the 19th century).

(10) Id. at 525 (citing A. Bulmerincq, Die Staatstreitigkeiten und ihre Entscheidung ohne Krieg, in 4 HOTZENDORFFS HANDBUCH DES VöLKERRCHTS 85, 87 (1889)).

(11) See Stephen W. Schwebel, The Reality of International Adjudication and Arbitration, 12 WILLIAMETTE J. INT'L L. & DISP. RESOL. 359, 364 (2004); HOWARD N. MEYER, THE WORLD COURT IN ACTION 1–2 (2002); V. S. Mani, Development of Effective Mechanism(s) for Settlement Disputes Arising in Relation to Space Commercialization, 5 SING. J. INT'L & COMP. L. 191, 193 (2001); Henry T. King & James D. Graham, Orgins of Modern International Abritration, 51 MARQUETTE DISP. RESOL. J. 42, 48 (1996).

(12) David D. Caron, War and International Adjudication: Reflections on the 1899 Peace Conference, 94 AJIL 4, 7 (2000).

(13) Id.; see also JOSEPH H. CHOATE, THE TWO HAGUE CONFERENCES 28–29 (1913).

(14) Leila Nadya Sadat, The Establishment of the International Criminal Court: From The Hague to Rome and Back Again, 8 J. INT'L L. & PRAC. 97, n. 1 (1999) (citing WILLIAM I. HULL, THE TWO HAGUE CONFERENCES AND THEIR CONTRIBUTIONS TO INTERNATIONAL LAW 3 (1908)).


(16) Convention for the Pacific Settlement of Disputes, art. 82, Oct. 18, 1907, 205 Consol. T.S. 233.

(17) Richard Ned Lebow, Accidents and Crises: The Dogger Bank Affair, 31 NAVAL. WAR. COL. REV. 66, 72–72 (1978).

(18) Convention of 1907 Respecting the Limitation of the Employment of Force for the Recovery of Contract Debts, Oct. 18, 1907, 36 Stat. 2241. Root did help establish the Central American Court of Justice in 1910. See 2 PHILIP C. JESSUP, ELIHU ROOT 511–12 (1937).



(21) Id. at 212.

(22) Id.

(23) Id. at 213.



(26) Article 10 provided:

The Members of the League undertake to respect and preserve as against external aggression the territorial integrity and existing political independence of all Members of the League. In case of any such aggression or in case of any threat or danger of such aggression the Council shall advise upon the means by which this obligation shall be fulfilled.

(27) Nico Schrijver, The Use of Economic Sanctions by the UN Security Council: An International Perspective, in INTERNATIONAL ECONOMIC LAW AND ARMED CONFLICT 123, 126–27 (Harry H.G. Post ed., 1994); 2 GARY C. HUFBAUER ET AL., ECONOMIC SANCTIONS RECONSIDERED: HISTORY AND CURRENT POLICY 17–28 (2d ed. 1990).

(28) Hans Kelsen, Contribution a l'étude de la révision juridico-technique du Statut de la Societé des Nations, 44 REV. GEN. DROIT INT'L PUBLIC 625, 649–51 (1937).

(29) Treaty for the Renunciation of War as an Instrument of National Policy, Aug. 27, 1928, 46 Stat. 2343, 94 LNTS 57. See also, IAN BROWNLIE, INTERNATIONAL LAW AND THE USE OF FORCE BY STATES 57 (1963).

(30) BROWNLIE, supra note 29, at 89. According to Röling: “‘Self-defense’ was regarded as embracing defence against nonviolent illegal impairment of interests.” Bert V.A. Röling, The Ban on the Use of Force and the U.N. Charter, in THE CURRENT LEGAL REGULATION OF THE USE OF FORCE 5 (Antonio Cassese ed., 1986).

(31) See, e.g., Locarno Treaty of Mutual Guarantee, Oct. 16, 1925, 54 LNTS 289.

(32) BROWNLIE, supra note 29, at 27.

(33) Alexandrov believes that measures short of force were generally considered to be subject to the Covenant, too, although there was some uncertainty about this. STANIMIR A. ALEXANDROV, SELF-DEFENSE AGAINST THE USE OF FORCE IN INTERNATIONAL LAW 38–39 (1996).


(35) BROWNLIE, supra note 29, at 222.


(37) UN Charter art. 2(4).

(38) BROWNLIE, supra note 29, at 112, 114.

(39) See UN Charter art. 51:

Nothing in the present Charter shall impair the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the UN, until the Security Council has taken measures necessary to maintain international peace and security. Measures taken by Members in the exercise of this right of self-defence shall be immediately reported to the Security Council and shall not in any way affect the authority and responsibility of the Security Council under the present Charter to take at any time such action as it deems necessary in order to maintain or restore international peace and security.

(40) Following the adoption of the UN Charter, the term war dropped out of fashion. War ministries became defense ministries. Most governments and scholars concluded that armed reprisals were no longer lawful even for law enforcement.

(41) See Albrecht Randelzhofer, Article 2(4), in THE CHARTER OF THE UNITED NATIONS: A COMMENTARY 112, 117 (Bruno Simma et al. eds., 2d ed. 2000.).

(42) Examples of economic coercion include economic embargoes, the termination of aid, or termination of sale contracts.

(43) Political coercion can take innumerable forms. The most common examples may be terminating diplomatic relations or official statements of denunciation.

(44) Physical coercion not involving armed force may include interdicting a river to a downstream state, deliberately setting a fire to cross a border, or cutting fishing nets.

(45) See, e.g., Michael N. Schmitt, Computer Network Attack and the Use of Force in International Law: Thoughts on a Normative Framework, 37 COLUM. J. TRANSNAT'L L. 885 (1999); see also George K. Walker, Information Warfare and Neutrality, 33 VAND. J. TRANSNAT'L L. 1079, 1177 n. 458 (2000) (quoting WALTER GARY SHARP, SR., CYBERSPACE AND THE USE OF FORCE 133 (1999): “Any computer network attack that intentionally causes any destructive effect within the sovereign territory of another state is an unlawful use of force within the meaning of [U.N. Charter,] Article 2(4) that may produce the effects of an armed attack prompting the right of self-defense.” Id.).

(46) Randelzhofer, supra note 41, at 117–21.

(47) See infra.

(48) BROWNLIE, supra note 29, at 265.

(49) 6 UNITED NATIONS CONFERENCE ON INTERNATIONAL ORGANIZATION 335 (1945). Brownlie concludes that at the San Francisco conference to draft the Charter, “[t]here was a presumption against self-help and even action in self-defence within Article 51 was made subject to control by the Security Council.” BROWNLIE, supra note 29, at 275 and references therein.

(50) UN Charter art. 39.

(51) Id. art. 45.


(53) See Covenant of the League, art. 13(4). Mary Ellen O'Connell, The Prospects for Enforcing Monetary Judgments of the International Court of Justice; A Study of Nicaragua's Judgment Against the United States, 30 VA. J. INT'L L. 891, 905–13 (1990).

(54) HANS KELSEN, PRINCIPLES OF INTERNATIONAL LAW 40–41 (R.W. Tucker ed., 2d rev. ed. 1966).

(55) Thomas Franck, Who Killed Article 2(4)? Or: Changing Norms Governing the Use of Force by States, 64 AJIL 809, 809 (1970).

(56) Id. at 810–11; see also for similar views, Jean Combacau, The Exception of Self-Defence in U.N. Practice, in THE CURRENT LEGAL REGULATION OF THE USE OF FORCE, supra note 56, at 9, 32 (footnotes omitted).

(57) Franck, supra note 55, at 835–36. After September 11, Franck wrote cogently on the application of UN Charter rules in light of the attacks of that day. See Thomas Franck, Terrorism and the Right of Self-Defense, 95 AJIL 839 (2001); see also THOMAS FRANCK, RECOURSE TO FORCE: STATE ACTION AGAINST THREATS AND ARMED ATTACKS (2002).

(58) Louis Henkin, The Reports of the Death of Article 2(4) Are Greatly Exaggerated, 65 AJIL 544, 545 (1971).

(59) Military and Paramilitary Activities in and Against Nicaragua (Nicar. v. U.S.), 1986 I.C.J. 14, para. 186 (June 27) [hereinafter Nicaragua].

(60) Michael J. Glennon, How War Left the Law Behind, N.Y. TIMES, NOV. 21, 2002, at A37; see also Michael J. Glennon, Preempting Terrorism: The Case for Anticipatory Self-Defense, WKLY. STANDARD, Jan. 28, 2002, at 24.

(61) CHRISTINE GRAY, INTERNATIONAL LAW AND THE USE OF FORCE 18 (2000). (This comment was apparently not repeated in the book's second edition in 2004.)

(62) Id.

(63) See Vienna Convention on the Law of Treaties, art. 31(3)(b), May 23, 1969, 1155 UNTS 331, 340.

(64) See Ian Brownlie, The Decisions of Political Organs of the United Nations and the Rule of Law, in ESSAYS IN HONOUR OF WANG TIEYA 91, 100–2 (Ronald St. J. Macdonald ed., 1994); W. Michael Reisman, The Constitutional Crisis in the United Nations, 87 AJIL 83, 96 (1993).

(65) See generally CHRISTINE GRAY, INTERNATIONAL LAW AND THE USE OF FORCE (2d ed. 2004) for support for this observation.

(66) See, e.g., Case Concerning Armed Activities on the Territory of the Congo, (Congo v. Uganda) 2005 I.C.J. (Dec. 19) [hereinafter Congo]; Oil Platforms (Iran v. U.S.), 2003 I.C.J. 161 (Nov. 6).

(67) 2005 World Summit Outcome, UN GAOR, 60th Sess., at 22–23, UN Doc. A/60/L.1 (Sept. 15, 2005) [hereinafter World Summit Outcome].

(68) Röling, supra note 30, at 3.

(69) UN Charter art. 51.

(70) ALEXANDROV, supra note 33, at 17.

(71) HANS KELSEN, GENERAL THEORY OF LAW AND STATE 333 (Anders Wedberg trans., 1945).

(72) See David Luban, Preventive War, 32 PHIL. & PUB. AFF. 207, 211–12 n.3 (2004).

(73) Luban may conflate the jus ad bellum (resort to war) and the jus in bello (conduct in war) in this observation.

(74) Mary Ellen O'Connell, Lawful Self-Defense to Terrorism, 63 U. PITT. L. REV. 889, 889–904 (2002). Measures taken in self-defense must be reported to the Security Council. Failure to do so brought into question the US claim that it was engaged in collective self-defense with El Salvador in the Nicaragua case. El Salvador had never reported to the Security Council that it was engaged in self-defense or had come under armed attack. Nicaragua, 1986 I.C.J. at 120–21, para. 233. The ICJ notes the same fact respecting Uganda's claim to have used force in self-defense against Congo. Congo, 2005 I.C.J. para. 145.

(75) Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territory, Advisory Opinion, 2004 I.C.J. 136, 215 (July 9) (Separate Opinion of Judge Higgins) [hereinafter Advisory Opinion on the Wall].

(76) See infra pp. 186–89.

(77) C. H. M. Waldock, The Regulation of the Use of Force by Individual States in International Law, 81 RECUEIL DES COURS 451, 498 (1952 II)(1968)(emphasis added).

(78) Lee A. Casey & David B. Rivkin, Jr., “Anticipatory” Self-Defense Against Terrorism is Legal (Dec. 14, 2001) (on file with the author); ANTHONY CLARK AREND & ROBERT J. BECK, INTERNATIONAL LAW AND THE USE OF FORCE: BEYOND THE CHARTER PARADIGM 186 (1993).

(79) Louis Henkin, Use of Force: Law and U.S. Policy, in RIGHT V. MIGHT: INTERNATIONAL LAW AND THE USE OF FORCE 37, 45 (Louis Henkin et al. eds., 1989).

(80) Id. at 53.

(81) Oscar Schachter, The Right of States to Use Armed Force, 82 MICH. L. REV. 1620, 1634–35 (1984)[hereinafter Schachter, The Right of States to Use Armed Force].

(82) John E. Noyes, The Caroline, in INTERNATIONAL LAW STORIES 263 (John E. Noyes et al. eds., 2007).

(83) Letter from Webster to Lord Ashburton (Aug. 6, 1842), available at The Caroline Case, http://www.yale.edu/lawweb/avalon/diplomacy/britain/br-1842d.htm.

(84) Schachter, The Right of States to Use Armed Force, supra note 81, at 1635.

(85) Nicaragua, 1986 I.C.J. at 100–1, para. 90.

(86) LOUIS HENKIN, HOW NATIONS BEHAVE 141 (2d ed. 1979); see also GRAY, INTERNATIONAL LAW AND THE USE OF FORCE (2d ed.), supra note 65, at 98–99; ALEXANDROV, supra note 33, at 165; Oscar Schachter, In Defense of International Rules on the Use of Force, 53 U. CHI. L. REV. 113, 133 (1986); Combacau, supra note 56, at 27–8; BROWNLIE, supra note 29, at 275–78.


(88) 1967 UN Y.B. 175–77. In reporting on its initial use of force Israel stated to the Security Council that that Egyptian forces had actually crossed into Israeli-held territory. By June 17, when the General Assembly began its debate on the conflict, Israel's foreign minister no longer spoke of actual Egyptian attacks but only of Egyptian forces approaching Israel's borders. 1967 UN Y.B. 196.

(89) Le général Rabin ne pense pas que Nasser voulait la guerre, LE MONDE, Feb. 19, 1968, at 1; see John Quigley, The United Nations Action Against Iraq: A Precedent for Israel's Arab Territories?, 2 DUKE J. COMP. & INT'L L. 195, 203–13 (1992).

(90) Nicaragua, 1986 I.C.J. at 14.

(91) The ICJ actually interpreted the meaning of Article 51 under customary international law, not as a UN Charter provision, but apparently there is no difference between the two. For analyses of this and other issues in the case, see, Mary Ellen O'Connell, The Nicaragua Case: Preserving World Peace and the World Court, in INTERNATIONAL LAW STORIES 339, supra note 82.

(92) Nicaragua, 1986 I.C.J. 103–04, at para. 195.

(93) Id. at 119, at para. 230.

(94) See G.A. Res. 3314, UN GAOR, 29th Sess., Supp. No. 31, at 142, UN Doc. A/9631 (1974).

(95) Id. See also SCHACHTER, supra note 52, at 117–23.

(96) Eritrea-Ethiopia Claims, Partial Award, Jus Ad Bellum, Ethiopia's Claims 1–8, Dec. 19, 2005, www.pca-cpa.org.

(97) Oil Platforms, 2003 I.C.J., at 186–7, para. 51.

(98) Mike Allen & Karen DeYoung, Bush: U.S. Will Strike First at Enemies; In West Point Speech, President Lays Out Broader U.S. Policy, WASH. POST, June 2, 2002, at A01. The speech did not go on to differentiate between “preemptive, unilateral military force” and “aggression.” Id.

(99) Available at http://www.defenselink.mil/execsec/adr2002/index.htm. Secretary of Defense Donald Rumsfeld stated in the report that, with regard to the lessons learned in the war on terrorism, “[D]efending the United States requires prevention and sometimes preemption. It is not possible to defend against every threat, in every place, at every conceivable time. The only good defense … is to take the war to the enemy. The best defense is a good offense.” Id. at 30.

(101) Available at http://www.whitehouse.gov/nsc/nss/2006/nss2006.pdf. In the political science community the terms “preventive” force or war are often used to describe the right claimed in the two national security strategies.

(102) See, e.g., John Yoo, Using Force, 71 U. CHI. L. REV. 729, 751–53 (2004).

(103) Henkin, Use of Force: Law and U.S. Policy, in RIGHT V. MIGHT, supra note 79, at 69.

(104) Richard B. Lillich, Humanitarian Intervention: A Reply to Ian Brownlie and a Plea for Constructive Alternatives, in LAW AND CIVIL WAR IN THE MODERN WORLD 229, 244–51 (John Norton Moore ed., 1974).

(105) Id. at 244–51.

(106) See Mary Ellen O'Connell, Enforcing the Prohibition on the Use of Force: The U.N.'s Response to Iraq's Invasion of Kuwait, 15 S. ILL. U. L.J. 453, 474–75 (1991).

(107) GRAY, INTERNATIONAL LAW AND THE USE OF FORCE (2d ed.) supra note 65, at 31; see also SIMON CHESTERMAN, JUST WAR OR JUST PEACE? (2001).


(109) 2005 World Summit Outcome,

  • (78.) We reiterate the importance of promoting and strengthening the multilateral process and of addressing international challenges and problems by strictly abiding by the Charter and the principles of international law, and further stress our commitment to multilateralism.

  • (79.) We reaffirm that the relevant provisions of the Charter are sufficient to address the full range of threats to international peace and security. We further reaffirm the authority of the Security Council to mandate coercive action to maintain and restore international peace and security. We stress the importance of acting in accordance with the purposes and principles of the Charter.

(110) See G.A. Res. 3314, art. 3:

Any of the following acts, regardless of a declaration of war, shall … qualify as an act of aggression: … (g) The sending by or on behalf of a State of armed bands, groups, irregulars or mercenaries, which carry out acts of armed force against another State of such gravity as to amount to the acts listed above, or its substantial involvement therein.


(111) Prosecutor v. Tadić, Case No. IT-94-1-A, Judgment, para. 137 (July 15, 1999).

(112) The ICJ found in the Nicaragua case that acts of the Contra rebels were not attributable to the United States because the United States did not exercise “effective control” over the rebels. Nicaragua, 1986 I.C.J., 64–65, at paras. 114–15.

(113) Id. Congo, 2005 I.C.J., at para. 345(1); Application of the Convention on the Prevention and Punishment of the Crime of Genocide, (Bosn. & Herz. v. Serb. & Mont.), 2007 I.C.J., at para. 391, available at http://www.icj-cij.org.

(114) Christiane Wirtz, Eine Discothek würde zum Kriegsschauplatz, Berliner Landgericht; Hochrangig Angehörige des libyschen Geheimdienstes planten den Anschlag, SüDDEUTSCHE ZEITUNG, NOV. 14, 2001, at 9.

(115) Christopher Greenwood, International Law and the United States' Air Operation Against Libya, 89 W. VA. L. REV. 933, 948 (1987).

(116) Edward Schumacher, Wide Damage Seen, Daughter of Qaddafiis Said to have Died, N.Y. TIMES, Apr. 16, 1986, at A1.

(117) Bernard Weinraub, U.S. Calls Libya Raid a Success; ‘Choice is Theirs,’ Regan Says; Moscow Cancels Schultz Talks, N.Y. TIMES, Apr. 16, 1986, at A1; see also Greenwood, supra note 115.

(118) Wirtz, supra note 114.

(119) Peter Finn, Libyan Convicted of Lockerbie Bombing; Second Man Acquitted In Attack on Pan Am 103, WASH. POST, Feb. 1, 2001, at A01.

(120) Mary Ellen O'Connell, Continuing Limits on UN Intervention in Civil War, 67 IN. L.J. 903, 905–6 (1992).

(121) Quoted in GRAY, INTERNATIONAL LAW AND THE USE OF FORCE 116 (2d ed.) supra note 65, at 116; see also Iran Claims Right of Self-Defence in Attacking Rebel Kurds, AGENCE FR.-PRESSE, July 30, 1996.

(122) Letter to the President of the Security Council, July 24, 1995, UN Doc. S/1995/605.

(123) GRAY, INTERNATIONAL LAW AND THE USE OF FORCE (2d ed.) supra note, at 116.

(124) Turkey Invades Northern Iraq, Economist, Feb. 28, 2008 available at http://www.economist.com/world/africa/displaystory.cfrm/story_id=10766808. See also Michael Bothe & Torsten Lohmann, Der türkisches Einmarsch im Nordirak, 5 SCHW. Z. INT'L. U. EUR. R. 441 (1995).

(125) Tim Weiner & Steven Lee Myers, After the Attacks: The Overview, Flaws in the U.S. Account Raise Questions on Strike in Sudan, N.Y. TIMES, Aug. 19, 1998, at A1; Paul Richter, Sudan Attacks Claim Faulty, U.S. Admits, L.A. TIMES, Sept. 1, 1998, at A1.

(126) William Drozdiak & Rajiv Chandrasekaran, NATO: U.S. Evidence on Bin Laden ‘Compelling’; Allies Give Unconditional Support for Retaliatory Strikes; Taliban Official Asks to See Proof, WASH. POST, OCT. 3, 2001, at A11.

(127) David Johnston & James Risen, Seized Afghan Files Show Intent, Not Plans, N.Y. TIMES, Feb. 1, 2002, at A13.

(128) See G.A. Res. 56/88, UN Doc. A/RES/56/88 (Jan. 24, 2002); S.C. Res. 1383, UN Doc. S/RES/1383 (Dec. 6, 2001); S.C. Res. 1378, UN Doc. S/RES/1378 (Nov. 14, 2001).

(129) Stephanie McCrummen, Ethiopian Premier Admits Errors on Somalia, WASH. POST, June 29, 2007, at A16.

(130) “Military operations in Somalia by American commandos, and the use of the Ethiopian Army as a surrogate force to root out operatives for Al Kaeda in the country, are a blueprint that Pentagon strategists say they hope to use more frequently in counterterrorism missions around the globe.” Mark Mazzetti, Pentagon Sees Covert Move in Somalia as Blueprint, N.Y. TIMES, Jan. 13, 2007, at A6.

(131) Id.

(132) Around the World, HOUSTON CHRON., Dec. 3, 2007, at A13.

(133) Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion, 1996 I.C.J. 226, 245, para. 41 (July 8) (quoting Nicaragua, 1986 I.C.J. at 94, para. 176) [hereinafter Nuclear Weapons]. See also Oil Platforms, 2003 I.C.J. 151.

(134) “States have a duty to refrain from acts of reprisal involving the use of force.” G.A. Res. 2625.

(135) Louis Henkin, International Law: Politics, Values and Functions, 216 RECUEIL DES COURS (1989 IV)(1991), revised and republished as, LOUIS HENKIN, INTERNATIONAL LAW: POLITICS, VALUES AND FUNCTIONS 159–62 (1990).

(136) D. Brian Hufford and Robert Malley, The War in Lebanon: The Waxing and Waning of International Norms, in INTERNATIONAL INCIDENTS 144, 176–78 (W. Michael Reisman & Andrew R. Willard eds., 1988).

(137) Serge Schmemann, U.N. Envoy Says All Options are Open on a Post-Taliban Afghanistan, N.Y. TIMES, Oct. 18, 2001, at B4.

(138) Letter to the President of the Security Council, UN Doc. S/2003/350 (Mar. 21, 2003).


(140) The right to use enforcement measures other than armed force appears to continue for very long periods. While it is generally acknowledged that international law includes the doctrine of laches, periods of forty, fifty, and more years have passed while states used countermeasures. See infra ch. 6.

(141) For the argument that claims continue in international law long after the initial wrong occurred, see John Quigley, Sovereignty in Jerusalem, 45 CATH. U. L. REV. 765 (1996).