As has been stressed before, not every use of force amounts to a violation of ius ad bellum. We will first examine the conditions of the lawful use of force, and then we shall characterize what a violation of ius ad bellum consists of.

1. Disregarding the Conditions of the Lawful use of Force

2. Legal Characterization of the Breach of Ius ad Bellum by a PMSC

The breach of ius ad bellum by a PMSC—that is, the unlawful use of force by a PMSC—can receive different legal characterizations, ranging from coercive intervention in the internal affairs of a state, to armed attack. As we will see later, the legal characterization of the breach of ius ad bellum varies according to the relationship between the state and the PMSC. It is well known that the notions (p. 401 ) of armed attack and aggression are left undefined by the UN Charter,²⁵ and were defined in 1974 by the UN General Assembly (UNGA).

In the distinct context of individual criminal liability, the definition of aggression given by the 1974 UNGA resolution has been further elaborated, challenged and confirmed. First, it was discussed and finally rejected by the ILC when working on a Draft Code of Crimes against the Peace and Security of Mankind.²⁶ Then, in the context of the creation of the International Criminal Court (ICC), the 1974 UNGA definition served as a basis for the definition of the crime of aggression in the Court's Statute. However, although included in Article 5 of the Statute of the International Criminal Court as a prosecutable offence, no definition of the crime of aggression could be agreed upon. The Special Working Group on the Crime of Aggression, established by the Assembly of the Parties to the Rome Statute to cope with the lack of definition of aggression in Article 5 of the Statute, presented a draft amendment to the Statute of the Court in February 2009.²⁷ The discussions of the Assembly of the Parties to the Rome Statute during the Review Conference of the Rome Statute, which was held in Kampala from 31 May to 11 June 2010, led to the adoption by consensus of a resolution on ‘The Crime of Aggression’, which confirms the pertinence of the 1974 UNGA resolution. Article 8 bis of the Statute is indeed introduced, and states:

1. For the purpose of this Statute, ‘crime of aggression’ means the planning, preparation, initiation or execution, by a person in a position effectively to exercise control over or to direct the political or military action of a State, of an act of aggression which, by its character, gravity and scale, constitutes a manifest violation of the Charter of the United Nations.

2. For the purpose of paragraph 1, ‘act of aggression’ means the use of armed force by a State against the sovereignty, territorial integrity or political independence of another State, or in any other manner inconsistent with the Charter of the United Nations. Any of the following acts, regardless of a declaration of war, shall, in accordance with United Nations General Assembly resolution 3314 (XXIX) of 14 December 1974, qualify as an act of aggression…²⁸

(p. 402 ) Although it is acknowledged here that the 1974 UNGA resolution definition of aggression is often considered unsatisfactory, and that the very aim of defining aggression has been challenged,²⁹ the 1974 UNGA proposal is still an incontrovertible element of the definition in our study.

According to resolution 3314 (XXIX), adopted by the UNGA in 1974: ‘Aggression is the use of force by a State against the sovereignty, the territorial integrity or political independence of another State, or in any other manner inconsistent with the Charter of the United Nations, as set out in this Definition.’³⁰ The resolution then provides for a list of cases considered as acts of aggression, such as wrongful attack, bombardment, blockade, etc.³¹ Article 3(g) of the 1974 resolution stipulates that an act of aggression can consist of: ‘The sending by or on behalf of a State of armed bands, groups, irregulars or mercenaries, which carry acts of armed forces against another State of such gravity as to amount to the acts listed above, or its substantial involvement therein.’³² Such a form of aggression is also referred to as indirect aggression, insofar as ‘the home State uses [the PMSCs] as a conduit (“on behalf of the State”) for indirect armed intervention against another State’.³³ Consequently, the resolution expressly recognizes that a PMSC can perform or contribute to an act of aggression by a state, when the conditions of legality of the missions we considered above are not met. This is indeed the position of the ICJ in the Nicaragua case, when dealing with the right of self-defence in customary international law, as reflected by Article 3(g) of the above mentioned 1974 resolution:

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 a threat or use of force, or amount to intervention in the internal or external affairs of other States.³⁴

The decision of the ICJ in the Nicaragua case has an impact on the legal characterization of acts that violate ius ad bellum, and that are attributable to a state, ranging (p. 403 ) from armed attack to mere intervention into the internal affairs of a state. According to the Nicaragua decision, a strong relationship—more than mere support—has to exist between the state and the PMSC in order for an armed attack to be attributed to the state. For instance, the case of peacekeeping operations based upon the consent of the territorial state is expressly foreseen in Article 3(e) of the 1974 Resolution of the UN General Assembly: ‘The use of the armed forces of one State, which are within the territory of another State, with the agreement of the receiving State, in contravention of the conditions provided for in the agreement or any extension of their presence in such territory beyond the termination of the agreement’³⁵ amounts to an act of aggression. This legal characterization of the aggression depends, as we will see in the next section, on attribution of the acts of PMSCs to the state and on their relationship—that is, whether the state is the contracting state, the territorial state, or the home state. A contrario, in cases where the state is only providing support to the acts of the PMSC personnel—where there is no close relationship between the state and the PMSC—only a threat or use of force, or a coercive intervention in the internal affairs of a State, could be attributed to the state, but not an act of aggression.

It must now be determined to what extent and in what conditions acts of PMSCs violating ius ad bellum can be considered acts of a state so as to trigger its international responsibility.

Two alternative criteria may be used to attribute breaches of ius ad bellum to a state.³⁶ In the first situation, when the PMSC exercises elements of governmental authority, and according to the conditions set up by the ICL Draft Articles, the behaviour of the PMSC is exclusively attributable to the contracting state (1). In the second case, the breach may be attributable to the contracting state, to the territorial state, or to the home state, provided the state either instructs the PMSC to act, or exercises direction or control over it (2).

1. Exercise of Elements of Governmental Authority

The criterion of the exercise of governmental authority is referred to in Article 5 of the ILC Draft Articles on State responsibility.³⁷ The preparatory works of the ILC³⁸ as well as the final commentary on the Draft Articles are useful, as they extensively refer to the case of PMSCs: the entities referred to:

(p. 404 ) may include public corporations, semi public entities, public agencies of various kinds and even, in special cases, private companies…For example, in some countries private security firms may be contracted to act as prison guards and in that capacity may exercise public powers such as powers of detention and discipline pursuant to a judicial sentence or to prison regulations. Private or State-owned airlines may have delegated to them certain powers in relation to immigration control or quarantine.³⁹

For the acts of a PMSC to be attributed to the state, two conditions have to be met: first, the PMSC has to be empowered by the law of the state; secondly, it has to be empowered to exercise elements of governmental authority.

The empowerment of the PMSC by the law of the state is a strict requirement, based upon the strength of the authorization that a sovereign state addresses to private groups through its legislative or executive organs.⁴⁰ In that respect, it is a widely accepted principle of international law that a state may be held internationally liable for its internal laws and regulations.⁴¹ Passing an Act of Parliament or adopting a regulation granting a PMSC the power to exercise part of the governmental authority is therefore the one and only condition necessary to link the future acts of the PMSC to the state. The ‘authorizing’ Act of the state consists in a limited delegation of the exercise of governmental or sovereign powers to a PMSC, which will enjoy a high degree of discretion when acting. Finally, one might wonder whether the internal authorizing Act of the state may be adopted either ex ante or ex post. In the latter case, the Act or regulation could be interpreted as expressing the consent of the state to endorse the acts that had already been perpetrated.⁴²

Secondly, the mandate should authorize the exercise of ‘governmental authority’. This concept is not defined by the ILC, and is expressly left to a case-by-case appreciation. However, in the situations we are dealing with here, which imply the use of force, and given the state-owned nature of defence activities, there is little doubt that the condition of governmental authority would be met. In this context, the fact that PMSC personnel wear arms could be one of the factors to consider. A contrario, in cases where a PMSC carries out a mixed activity (ie military and commercial), only the part amounting to the exercise of governmental authority would be attributable to the state under Draft Article 5. The question then follows of the attribution to the state of ultra vires acts of PMSC personnel whilst exercising elements of governmental authority. As recalled in the Commentary of Draft Article 7 ICL, the rule according to which the conduct of an entity empowered to exercise elements of governmental authority is to be attributed to the state, is a well-recognized customary norm of international law.⁴³ In other words, all acts of the PMSC are to be attributed to the empowering state, if, and only if, these ultra (p. 405 ) vires acts can still be linked to the delegated governmental functions. In this case, the PMSC is treated as if it were an organ of the state.

In practice, as has already been shown in the context of the Priv-war project, the criterion of the existence of a national act empowering a PMSC is problematic. Indeed, H Cherif mentioned in his report a case of arbitration in Papua New Guinea, where the Tribunal refused to interpret the constitutional provision regulating the raising of special forces, which required the prior adoption of an Act of Parliament. In the main, the Tribunal argued that the interpretation of the constitution had to be left to national courts. However, despite the fact that in this case the PMSC had not been previously empowered by an Act of Parliament, the contract was considered valid in international law.⁴⁴

Our conclusion on the attribution to a state of acts of a PMSC under Draft Article 5 is twofold. First, in terms of the relationship between the PMSC and the state, it appears that acts of a PMSC can only be attributed to the contracting state. As we have demonstrated, the requirements of Draft Article 5 are even stricter, since the state not only has to be contracting with a PMSC, but also has to do so by virtue of its own law. This of course does not exclude the purely practical possibility that the contracting state is also the home state. Similarly one could imagine, in the case of self-defence operations, that the contracting state might also be the territorial state. Secondly, in terms of the legal characterization of the acts of the PMSC, which violate ius ad bellum, it should be stressed that it is only where a PMSC exercises elements of governmental authority that an act of aggression can with certainty be attributed to the state. As we showed in the previous section when examining the definition of an act of aggression, the ICJ considers that mere support by a state to armed groups would not suffice to attribute responsibility for an armed attack to the supporting state. Rather, the actions of the PMSC would need to be on a large scale, and the relationship between the state and the PMSC the strongest possible.⁴⁵ This strong relationship would be characterized here by the empowering Act or regulation enacted by the state.⁴⁶

2. Instructions, Direction, or Control

We now turn to the examination of Draft Article 8, which sets up the other criterion for attributing the conduct of a PMSC to a state: instruction, direction, or control—these three conditions being understood as a gradation, from a (p. 406 ) concrete action on the part of the state (giving instructions), to a legal fiction linking acts to a state (directing and controlling troops).

The most straightforward situation falling within the scope of Draft Article 8 is instruction, when the state de facto requires PMSC personnel to adopt certain behaviours in breach of ius ad bellum. An example of this is given in the Commentary of the Article itself, where private persons or groups are recruited by the state and act as ‘auxiliaries’ without being part of the regular forces of the state.

Two international courts have given different interpretations to the criterion of ‘direction and control’ by a state.⁴⁷ The ICJ first interpreted restrictively the criterion of ‘effective control’ in the Nicaragua case, when examining the activities of military forces in Nicaragua: ‘such acts could well be committed by members of the contras without the control of the United States. For this conduct to give rise to legal responsibility of the United States, it would in principle have to be proved that that State had effective control of the military or paramilitary operations in the course of which the alleged violations were committed.’⁴⁸ More than ten years later, in the context of individual criminal responsibility, the International Tribunal for the former Yugoslavia (ICTY) expressly disagreed with the standard set up by the ICJ in the context of state responsibility, considering that ‘The degree of control may…vary according to the factual circumstances of each case.’⁴⁹ Since then, however, the ICJ has twice confirmed its interpretation of the criterion of ‘effective control’ in order to establish state responsibility; in 2005 in the Case Concerning Armed Activities on the Territory of the Congo,⁵⁰ and in 2007 in the Genocide case. In the latter case the Court clarified its position: ‘the particular characteristics of genocide do not justify the Court in departing from the criterion elaborated in the Judgment in the case concerning Military and Paramilitary Activities in and against Nicaragua…The rules for attributing alleged internationally wrongful conduct to a State do not vary with the nature of the wrongful act in question in the absence of a clearly expressed lex specialis.’⁵¹

Then one must ask whether or not ultra vires acts can be attributed to a state. When a state authorizes, directs, or controls the acts of PMSC personnel, but the addressees go beyond those orders or directions, the ultra vires acts can nevertheless be attributed to the state if they remain connected to the mission. Indeed, as the Commentary on Draft Article 8 stresses, an ultra vires act will still be attributable to the state, although ‘particular instructions may have been ignored’.⁵²

(p. 407 ) In considering the relationship of the state to the PMSC, the criterion of instruction, direction or control can apply in order to attribute PMSC acts to the territorial state and the home state as well as to the contracting state.⁵³ On the other hand, however, the legal characterization of attributable acts is more restricted. Indeed, as has already been demonstrated when examining the definition of acts of aggression⁵⁴ and the exercise of elements of governmental authority,⁵⁵ in order to attribute to the state PMSC acts that would qualify as an armed attack, a strong relationship between the state and the PMSC is needed, mere control by the state not being sufficient. It is thus very unlikely that acts of a PMSC amounting to acts of aggression could be attributable to a state under the criterion of instruction, direction, and control. Accordingly, where a state simply supports the actions of a PMSC, it would be possible to attribute to that state a threat or use of force, or an intervention in the internal affairs of a state but not an act of aggression.

In conclusion, the establishment of state responsibility for acts of PMSCs violating ius ad bellum stricto sensu is subject to very strict conditions. First, a violation of ius ad bellum has to be ascertained, which can prove rather difficult in situations where it is claimed to be abiding with the conditions of lawful self-defence operations, peace operations, or humanitarian interventions.

Secondly, the acts violating ius ad bellum have to be attributed to a state under one of the alternative criteria set up by Draft Articles 5 and 8 ICL. As we have just demonstrated, the range of states (contracting, home, or territorial) to which the acts can be attributed, as well as the legal characterization of the breaches of ius ad bellum, are highly variable according to the concrete situation at hand. It follows from this that state responsibility for acts of PMSCs violating ius ad bellum should also be looked at lato sensu, from the perspective of the existence of an obligation of due diligence imposed on the state. In such a case the international wrongful act attributable to the state would no longer be a breach of ius ad bellum in the sense discussed above, but could rather be characterized as a breach of an extended ius ad bellum embracing a positive obligation not to allow PMSCs to commit acts amounting to violations of ius ad bellum.

As an illustration, let us assume that a PMSC, X, is contracting with a rebel group operating from state A to participate in hostilities against state B. X participated in an attempted coup against the political leader of state B. The rebel group and X's forces ambushed the presidential convoy during a visit of the leader of state B in a district close to the frontier with state A. The head of state of state B was not killed; however 15 soldiers were killed and 30 wounded. We know Article 2(4) of the Charter of the UN prohibits the threat or use of force against the territorial integrity or political independence of any state.⁵⁶ Suppose that the PMSC in question is present on the territory of state A but is incorporated and having its principle place of management in another state. In sum, state A had no direct control or involvement in the activities of X. Then, under which circumstances and on what grounds could the above act constitute a breach of an international norm? Could this breach be attributed to state A? Could the state of incorporation or any other state also be held responsible for the abovementioned private acts? Did those states fail to abide by their duty to protect state B?

1. Identifying the Due-diligence Principle

The International Law Commission has discussed at length the question of state responsibility with regards to the activities of private persons. For instance, in its commentaries on the Draft Articles on State Responsibility, and under the influence of Roberto Ago, the ILC stated in 1975 that:

The strictly negative conclusion reached regarding the attribution to the State of the acts of private natural and legal persons and of the other persons…does not imply, however, that the State cannot incur international responsibility for such acts on other grounds….A State has often been held internationally responsible on the occasion of acts or omissions whose material perpetrator was a private natural or legal person who, on that occasion, was not acting on the State's behalf.⁵⁷

Depending on the particular facts and circumstances of a case, a ‘failed act’ or omission of state authorities may constitute a breach of what had been lawfully (p. 409 ) expected of them with regard to the activities of persons or companies over which state organs have regulatory power.⁵⁸ In other words, thanks to what is called the due-diligence principle under international law, a state may be held accountable for prima facie private acts that cannot be directly attributed to a state. Simply stated, the due-diligence obligation is then ‘the degree of care…expected of a good government’.⁵⁹ The principle is based on general international law and can be applied to several facts and circumstances. In our case, however, more specific provisions of international law can also be appropriate when determining the due-diligence obligations regarding PMSCs' activities.

The first main international decision stating the due-diligence principle was taken in the Island of Palmas case. In the opinion of the sole arbitrator, Max Huber, territorial sovereignty has as a corollary duty ‘the obligation to protect within the territory the rights of other States, in particular their right to integrity and inviolability in peace and in war’.⁶⁰ Among several decisions on the issue, the ICJ, in the famous Corfu Channel case, also stated ‘every State's obligation not to allow knowingly its territory to be used for acts contrary to the rights of other States’ as a general and well-recognized principle, linked to ‘elementary considerations of humanity, even more exacting in peace than in war’.⁶¹ The protection of the rights of other states does not mean that every state incurs responsibility simply because the rights in question are disregarded. Nonetheless, focusing on the violation of the Convention on the Prevention and Punishment of the Crime of Genocide, the ICJ recalled that ‘responsibility is however incurred if the state manifestly failed to take all measures to prevent genocide which were within its power, and which might have contributed to preventing the genocide’.⁶² Due to the separation between international and national legal orders, and because the former cannot directly rule the latter, it is necessary to attribute to the state all that happened in the domestic order from the moment that the state in question could have prevented the damage caused to another sovereign.

Nowadays, the due-diligence principle is often invoked with regards to environmental harms and, since 9/11, to the failure to prevent terrorist activities taking (p. 410 ) place within a state's territory.⁶³ Back to our case study, it means that state A may be held accountable for a breach of the due diligence principle because PMSC X had planned to perpetrate a coup from the territory of state A. General international law requires from state a kind of ‘obligation de s'efforcer’ to prevent any attack from its territory on state B.⁶⁴ As Pierre-Marie Dupuy has stated, ‘what counts here is the violation of the best effort obligation, not the end result actually achieved’.⁶⁵ If one can establish, for instance, that state A had the means to regulate activities of PMSC X, the breach would be manifest.⁶⁶

International law may be relevant in certain scenarios involving the use of PMSCs even though a customary prohibition of the use of mercenaries cannot be easily established. It is therefore interesting to explore whether any international agreements contain an obligation to prevent that could be applicable to our case or to other private misconducts. For instance, considering the responsibility of the home state or of the state in which the company operates from, the law of armed conflict could be seen as implicitly prohibiting mercenary activities on the territory of neutral powers.⁶⁷ If a PMSC operates from the territory of a neutral power and participates from this territory in hostilities between belligerents, the responsibility of the neutral power may be engaged for a violation of an obligation to ‘not allow any of the acts referred to in Articles 2 to 4 to occur on its territory’, based on Article 5 of the 1907 Hague Convention V.⁶⁸ At least two other texts may be helpful in this context: Article 3 of the Convention on the Protection and Punishment of Crimes against Internationally Protected Persons, including Diplomatic Agents; and Article 15 of the International Convention for the Suppression of Terrorist Bombings.⁶⁹ However, there is a lack of relevant jurisprudence that (p. 411 ) illustrates the practical application of the above provisions. The violation of the obligation of due diligence could be based on particular international laws related to PMSCs or more generally to terrorist activities. Among the rare treaties on the issue, there does not seem to be any relevant Article on the due-diligence principle.⁷⁰ The Montreux Document appears more appropriate in this regard, but ‘is not a legally binding document’.⁷¹ Therefore, to date, any allegation of a violation of its terms is irrelevant—except when it restates pre-existing human rights and international humanitarian law obligations.⁷² The same could be said for two other draft conventions: the Draft International Convention on PMSCs, elaborated in 2008, and the Draft International Convention on the Regulation, Oversight and Monitoring of PMSCs, proposed in 2009.⁷³

2. Applying the Due-diligence Principle

The concrete application of the due-diligence principle may not be an easy task, given the relative vagueness of the obligation. Whether the breach is based on general international law or on rare but appropriate treaties, the lack of vigilance of a state remains to be proven. The plaintiff would have to show evidence that a state failed to act with due diligence regarding the activities of a PMSC, and such evidence might be hard to obtain. What is concretely expected from a ‘well governed’ state with regards to the PMSCs operating on its territory or incorporated under its laws? How does one reveal any failure?

There is a lack of relevant case law regarding due diligence within the ius ad bellum or ius contra bellum corpus. In any case, the due-diligence principle calls for an assessment in concreto.⁷⁴ In the Corfu Channel case, the ICJ assessed that even considering the reality of ‘exclusive territorial control’, the territorial state need not (p. 412 ) necessarily know that private actors are likely to commit unlawful acts.⁷⁵ In sum, the international judge or arbiter would have to assess the facts and circumstances of each allegation. The position would depend upon a precise analysis of which norms apply in each case, and it is clear that there are not many specific norms concerning the relationship between states' policies and PMSCs. One would have to compare the content of the general or particular norm in question with both the wish and the means of a state to act, and take into account—but not decisively—whether the acts occur on the territory of the state in question. There has recently been, for instance, much debate about the Taliban government of Afghanistan's inaction concerning Al-Qaeda training camps or Lebanon's inaction vis-à-vis Hezbollah activities.⁷⁶

In sum, the riskier the situation in which PMSCs are tolerated, the stronger due-diligence obligation for the territorial state is. In our case study, one would probably consider that state A should have known the activities of PMSC X, a fortiori in a troubled area where rebel groups are supposed to be carefully monitored. Any PMSC which aims to participate in hostilities needs to import military equipment, money, or personnel, and it is doubtful that the state whose territory hosts the PMSC and the preparation of an attack could ignore it. In any event, if it cannot act to effectively control the PMSC's activities, it has a duty to inform the other state(s) which may be the target of an attack. The home state should also be aware of any large operation that its PMSCs are dealing with. Moreover, going beyond due diligence stricto sensu, the more general principle of the responsibility to protect could also imply, as a corollary, a duty to sanction any abuses actually that would have happened.⁷⁷ Suppose, for instance, that the state where the acts occurred had refused to investigate on the facts or refused to prosecute the authors (and on appropriate grounds), the state would also have violated its obligations to prosecute and punish—based upon appropriate personal or territorial jurisdiction, universal jurisdiction or on the aut dedere aut prosequi rule.⁷⁸ The European Court of Human Rights has found that states can be held responsible for their failure to conduct a proper investigation regarding violence perpetrated by private actors.⁷⁹ Therefore, both the home and territorial states should be considered in a position to prosecute PMSCs as such or individuals that would be accused of grave misconducts. After all, general prevention is one of the main objectives of any justice (p. 413 ) system and this applies equally when a rebel group or a PMSC plans to commit an armed attack against a state.

To conclude, the due-diligence principle in international law must not be considered an empty legal concept because of its vagueness. Regarding PMSCs' activities and particularly their direct participation in hostilities, the obligation to prevent has a role to play in holding states responsible in relation to private acts that were at least tolerated by the home state or the territorial state. In this field, however, the due-diligence principle is so far mainly based on general international law. Considering the subjectivity of the due-diligence test, it may be appropriate for every state to adopt good practices or precautionary measures vis-à-vis PMSCs that are operating on their territory, with their nationals, or that are incorporated in their jurisdiction. For instance, one would think of a system of ex ante licences for the creation and operations of PMSCs or the creation of authorization and monitoring procedures for exporting any PMSCs services.⁸⁰ The good state practices identified by the Swiss Initiative may be helpful but they are not exhaustive.⁸¹ In any case, due diligence should be seen as an appropriate tool to encourage more regulation and lead to less abuse.

We will now turn to drawing the consequences of the above demonstration in terms of the domestic law of the state. Indeed, we first established the conditions for holding a state responsible for the acts of PMSCs violating ius ad bellum. It was then showed how the principle of due diligence in public international law imposes positive obligations on both territorial and home states in order to ensure that the prohibition of the use of force in international law is respected by the PMSCs.

For the sake of consistency, it necessary that a state take the appropriate steps in its internal legal order to ensure the respect of its international obligations. In the context of state responsibility for the acts of PMSCs violating ius ad bellum, the state is therefore bound to prohibit, in its domestic order, the perpetration of any violation of ius ad bellum by private actors. Such uniform law provisions, accompanied with more precise obligations of the states, could eventually lead to establish state responsibility for the lack of domestic regulation leading to the perpetration of such acts by the PMSCs. It is not the aim of this chapter to address individual criminal liability. Although the natural setting of such a domestic regulation is (p. 414 ) domestic criminal law, we will only focus here on the state duty to regulate, as the necessary corollary of its obligation to ensure that the prohibition of the use of force in public international law is complied with.⁸²

1. Prohibiting in the National Legal Order any Violation of Ius ad Bellum by PMSCs

It is held here that as soon as an obligation to prevent and repress crimes of private actors arises in international law, it necessarily implies that the state should enact a criminal law prohibiting this specific activity in its national legal order and providing jurisdiction to its organs, in order to fulfil its international engagements. Although both elements would be provided for in the same national legal instrument, the substantive norm will be distinguished from the competence norm⁸³ in this exposé.

From the substantive perspective, the national legal order should be compatible with the state's international obligations, and more precisely, with the obligation to prevent and repress international crimes. As the Permanent Court of International Justice (the PCIJ) said in a well-known advisory opinion, a state which has contracted valid international obligations is bound to make in its legislation such modifications as may be necessary to ensure the fulfilment of the obligations undertaken.⁸⁴ It certainly does not stem from this, that a state may be held responsible at an early stage, for not bringing his national legal order into conformity with his international obligations. It is however clear that, in some situations, international law requires the state to take positive steps, for example, when the only way to respect the international obligation implies the enactment of a specific norm, or when such an enactment is clearly required by a written instrument such as a uniform law treaty. Therefore, a substantive norm of the domestic legal system prohibiting crimes recognized in international law, participates in the fulfilment of a state's international criminal obligations. Admittedly, this obligation goes beyond a simple obligation to prevent and repress. Uniform law obligations must also be consistent with international criminal law. Indeed, in a legally constituted state, a criminal penalty can never be applied to a subject of domestic law without a specific provision of the law commending it. This derives from the nullum crimen sine lege principle, which is also recognized as a general principle of international law.

Furthermore, this obligation to enact a kind of uniform criminal law could arise from the ius cogens nature of the prohibition of certain behaviours. We can easily imagine that if the obligation to prevent and repress private actors' acts were attached to a ius cogens prohibition, this would further result in a positive (p. 415 ) obligation for states to put their national legal orders in conformity with it.⁸⁵ This appears particularly clearly from the words of the ICTY in the Furundjiza case, regarding the prohibition of torture. It was indeed asserted that: ‘States are bound to put in place all those measures that may pre-empt the perpetration of torture.’⁸⁶ This interpretation undoubtedly derived from the gravity of the crime of torture, and the ius cogens nature of its prohibition.

We now turn to apply the above reasoning to the prohibition of the use of armed force. It is clear that states should have enacted a criminal law prohibiting the use of armed force to their nationals and/or residents, in order to be in position to repress such a crime. For instance, armed attack is recognized as a crime in international law, as suggested in UN General Assembly Resolution 3314.⁸⁷ Moreover, according to Article 5 ICC Statute, armed attack is a potential crime entering the competence of the Court. In contradistinction with the obligation to prohibit torture, no written rule on the obligation to prohibit the use of force in international relations by private actors is entrenched in a conventional instrument. Approximating rules can nevertheless easily be found in other instruments, as it is the case regarding the prohibition of mercenarism. To give an example, the OUA Convention imposes an obligation on states to prohibit, not only in the civil branch but also in the criminal sector, since: ‘Each contracting State shall undertake to make the offence defined Article 1 of this Convention punishable by the severest penalties under its laws including capital punishment.’⁸⁸ Similarly, the UN Convention on Mercenarism, reads that states ‘shall make the offences set forth in the present Convention punishable by appropriate penalties which take into account the grave nature of those offences’.⁸⁹ The obligation to prohibit is, here again, inducted by the importance of the prohibition itself, which is not under discussion regarding the ius ad bellum primary rules.

The principal hurdle in our case is the difficulty for states to agree upon a precise definition of armed attack, especially after the 9/11 events. Indeed, how could it be (p. 416 ) possible to press states to put their national legal order into conformity with international law, when international law itself may have appeared unclear? This obstacle may be overcome. First, it cannot be said that there is a total lack of definition of aggression in international law, since the very aim of Resolution 3314 (XXIX) of the UN General Assembly is to attempt to provide one.⁹⁰ However, there is no denying the fact that an international tribunal cannot be competent to prosecute a crime until an agreement between states parties on a very precise definition of it has occurred: the international nature of this jurisdiction derives from the will of its states parties. This does not, however, affect the binding effect of the prohibition of the use of armed force on states themselves, or their subsequent duty to prevent violations of ius ad bellum—be it in the form of armed attacks against other states by their nationals, and/or from their territory. Simply, the definition of the crime they have to prosecute at a national level is not internationally set, and states—and more precisely their parliaments—are free to provide one of their own, as long as it is compatible with the few existing international guidelines. It is thus only a question of measure, and although it is not possible to identify a real uniform-law obligation binding states to unify their laws on a precise model, it can still be defended that states have to harmonize their national criminal legal orders with the international prohibition of using armed force in international relations. This illustrates the distinction between an obligation to unify and an obligation to harmonize.⁹¹

Going back to the specific issue of PMSCs, the question arises whether states do need to prohibit the violations of ius ad bellum for PMSCs in particular, or whether these private companies would simply fall into the scope of the criminal law that states should already provide for, according to their general duty to implement in their domestic system international law obligations to prosecute and punish breaches of ius ad bellum. If states have to prohibit the international illicit use of force in their national legal systems, do PMSCs fall in the scope of these legislations? A difficulty may arise from the possible military status that could be granted by some states to those companies.⁹² Indeed, such a qualification would exclude the criminal liability of the companies and their personnel, even in the case of direct participation in an armed attack against another state.⁹³ State responsibility for the violation of the ius ad bellum does not only include the use of force attributable to the state itself. Even if the use of force is attributable to the state, the latter must still (p. 417 ) prosecute among its organs, delegated or controlled entities, those who are personally responsible for the international crime.

To conclude, on the obligation for states to prohibit the use of armed force by PMSCs, no internationally binding instrument specifically refers to those companies, although written obligations to prohibit exist on related matters. One could argue that an international customary rule could gradually arise from the state's domestic prohibition of the use of armed force by PMSCs, since many states actually prohibit such behaviour.⁹⁴ However, as already shown, no uniform states practice can be identified at present on this matter. Only international instruments without any binding force are clearly following this path, for example, the Montreux Document⁹⁵ and the Draft International Convention on the regulation, oversight and monitoring of PMSCs.⁹⁶

2. Uniform-law Obligations: Going Further

A new question arises at this stage of our study: which is the competent state to prosecute those crimes? And is this issue regulated by international law? After having answered these questions, this chapter will examine whether new obligations related to ius ad bellum and regarding the national regulation of PMSCs could be directed to specific states.

On the question of state competence to prosecute the crimes connected to the use of force by PMSCs, no clear-cut solution is possible, since international law only urges states not to let those crimes go unpunished. Some could have accepted their jurisdiction on a universal basis, even without personal or territorial link to the case, as soon as the alleged criminal is found on their territory, as is the case for torture for instance.⁹⁷ In any case, usually, the conflicts of competences at stake remain in a latent form. In sum, it is as if the maxim ‘the more the merrier’ could apply to this issue. One knows that states are often very jealous of their jurisdiction, (p. 418 ) as shown by the affairs involving Belgium and the Congo.⁹⁸ We could imagine that international law would forbid states from granting immunity to an alleged criminal but it is improbable that international law could go any further and oblige states to provide for specific competence norms in their national legal order. Needless to say, no uniform-law obligation can be found in those questions of jurisdiction, which are, as part of the constitutional organization of states, left at their total discretion. The obligation to prosecute may give birth to an obligation to prohibit the said crime in the national legal order in a substantive way, but it is difficult to foresee how any obligation to regulate national competence rules could arise from it. International law does not aim at regulating states' competence, but only its exercise.⁹⁹

If no uniform law on competence can be found, are there, nevertheless, specific rules which could solve the problem sketched above? In other words, if international law does not attempt to regulate states' jurisdiction, is there any rule aiming at regulating the legal framework of PMSCs? Until now, we have only showed the existence of a general obligation to prohibit certain behaviour, an obligation which is not directed to any state in particular. Since then, conflicts of jurisdiction between concerned states, or even lack of jurisdiction, are likely to occur. The violations of ius ad bellum are not necessarily considered crimes in international law. Nonetheless, states still have to prevent those acts committed by private actors. Then, specific uniform-law norms, going beyond the prohibition of crime of aggression, could be very useful to construe ius ad bellum as a whole. Needless to say, nothing of this kind could currently exist in international customary law, since problems arising from the use of PMSCs are too new. Nevertheless, clues could be given by the existing international conventions, even if they do not exactly refer to private companies and focus instead on mercenarism. The aforementioned Montreux Document often confirms these considerations as regards the PMSCs. From these several dispositions, directives for a more precise uniform law instrument could arise. States would still have to agree upon them at a second stage, in order to be bound to put their national legal orders into conformity with them.

Regarding contracting states, it is hard to find any obligation above a general prohibition on using PMSCs in order to violate the ius ad bellum. A criterion for the contracting state should be that the PMSC should not be aiming at violating the rules on lawful use of force. The interest of this criterion is that responsibility could arise from the mere fact of concluding a contract with a PMSC in order to violate international law, with no need to wait for any concrete armed attack. Concerning the home state, specific obligations could be put on them when they are neutral, according to the Hague Convention on Neutral Powers.¹⁰⁰ Article 4 of this treaty (p. 419 ) forbids the formation of combatants and even more precisely the opening of ‘recruiting agencies on the territory of a neutral Power to assist the belligerents’. Before any concrete violation of the ius ad bellum by a private company, a neutral state should be held responsible for the mere incorporation of a company of this kind in his territory and, even before that, for the mere fact that its national legal order allows such an incorporation. This is also true for states contracting with mercenaries, according to the OUA Convention. In any case, home states should ‘harmonise their authorisation system and decisions with those of other States and taking into account regional approaches relating to authorisation systems’.¹⁰¹ We can easily infer from this that a uniform private law on companies should be adopted by way of an international convention. It should be directed to home states in order to determine which activities a PMSC has the right to propose and the authorizations it must obtain.¹⁰² In the perspective of the prevention of violations of ius ad bellum, this uniform-law obligation can be seen as part of the ius ad bellum binding upon home states.

Territorial states have also duties deriving from the Hague Convention when they belong to the category of neutral power. Indeed, since belligerents are forbidden by this treaty ‘to move troops or convoys of either munitions of war or supplies across the territory of a neutral Power’,¹⁰³ a neutral state has to prohibit PMSCs from acting from its territory and needs probably to bring its legal order into conformity with this obligation. This does not seem, however, to further the obligation to prohibit the use of force in international relations, that we evidenced above.