Multiple legal regimes apply to parties and co-parties to an armed conflict. This chapter discusses what co-party status means for the application of the different bodies of international law, and how those bodies of law interact.
3.1 Party status and the ius ad bellum
Concerns in governments and among their domestic audiences over becoming a party to an inter-state armed conflict seem to be driven on occasion by the view that this would entitle the adverse party to use force against them. Avoiding the perception of being ‘at war’ with another state may be an important factor in assessing the escalatory potential of one’s action. And it may be an important political consideration. Valid as they may be, however, these military and political concerns should be distinguished from the legality of the use of force by or against states that are parties to an (international) armed conflict.
Article 2(4) of the UN Charter and customary international law prohibit the use of force by one state against another, subject to narrowly confined exceptions of individual or collective self-defence and authorization by the UN Security Council (UNSC). The prohibition of the use of force also applies between states that are parties to an IAC. Under international law, therefore, a state that is party to an IAC may only use force against another state which becomes a party to that IAC on the adverse side if that force is permitted by self-defence or authorized by UNSC resolution.
If a state joins an armed conflict as a party on the side of the state subject to an armed attack which has sought its help, its actions would be justified by collective self-defence, provided it kept within the confines of necessity and proportionality. In such a case, the adverse (aggressor) state may not lawfully use force against it.
To be clear, therefore, it is not because a state becomes a party to an armed conflict that it may use force, or have force used against it, under the ius ad bellum. If a supporting state joins in hostilities to such an extent that it becomes a party to the conflict, that in itself does not authorize the adverse state to attack it. If the supporting state uses force on the side of the aggressor, then the adverse party is entitled to exercise self-defence against the aggressor. But if the supporting state is joining in lawful self-defence, then the adverse party has no right to attack the supporting state – there is no right of self-defence against a lawful act of self-defence.
It is not because a state becomes a party to an armed conflict that it may use force, or have force used against it, under the ius ad bellum. If a supporting state joins in hostilities to such an extent that it becomes a party to the conflict, that in itself does not authorize the adverse state to attack it.
Becoming a party may, however, have consequences for the legality of targeting under the ius in bello. When a state becomes a party, it generally is not considered a violation of the ius in bello to target members of that state’s armed forces. That assessment does not affect, and is not affected by, whether or not the act in question constitutes a lawful or an unlawful use of force under the ius ad bellum. Still, the practical significance of the ius in bello assessment should not be underestimated. Frequently, both sides – rightly or wrongly – consider themselves to be acting in conformity with the ius ad bellum. In such situations, the decision of whether force may lawfully be used against a particular individual should be driven by whether or not that individual is targetable under the ius in bello. More generally, the ius in bello assessment is important for its more specific guidance on how force is to be used on the battlefield. It is also crucial for establishing whether or not individuals who act on the battlefield violate international law (and, potentially, commit war crimes), since individuals are bound by certain ius in bello rules, while the ius ad bellum only applies between states.
In sum, the ius ad bellum and the ius in bello apply to states that are parties to IACs in parallel. Although the ius ad bellum applies without regard to the respective states’ party status, the following sections show that party status remains central to the regulation of contemporary armed conflicts in many respects.
3.2 Party status and the ius in bello/IHL
Under IHL, party status is relevant on several levels.
Parties’ obligations and ‘rights’
It is the parties who bear the primary responsibility for ensuring that the conflict is carried out in accordance with international law. Parties to international, as well as non-international, armed conflicts have many obligations under IHL, both regarding the means and methods of warfare and on the protection of individuals. For example, it is the parties that have the obligation to distinguish combatants and military objectives from civilians and civilian objects in the conduct of hostilities, as well as the obligation to care for the wounded and sick. And, if there are multiple parties on the same side of an armed conflict, the obligations flowing from party status also translate into particular positive duties regarding the conduct of their partners in the conflict.
In addition, parties to an IAC historically enjoyed ‘belligerent rights’. These included the establishment of blockades, searching and seizing vessels for contraband and using self-help against neutrals violating their obligations under the law of neutrality. While ancient, these rights still play a certain role in state practice. Yet, to the extent that they would permit the use of force, exercising these rights would today also attract the ius ad bellum prohibition on the use of force. The relationship between these rules and the ius ad bellum is not settled in international practice. It appears to be consistent with the current structure of the international legal order, however, that the prohibition of the use of force circumscribes the exercise of these rights. In other words, they cannot grant any permissions that extend beyond what would be permissible for the respective state under the ius ad bellum. As noted below, however, party status may have certain permissive effects under other rules of IHL, notably those of the law of targeting and detention, as well under IHRL.
Parties and the protection of individuals
Beyond bearing obligations and rights, parties are also relevant as reference points in determining which rules apply to individuals engaged in or affected by armed conflict. This is chiefly the case regarding combatants, who are defined as members of the armed forces of a party, and who are therefore targetable under IHL, but also have obligations under IHL in relation to matters such as the conduct of hostilities and the treatment of prisoners of war. In addition, many categories of individuals protected under IHL are defined by their connection to a party to the conflict – for example, prisoners of war or individuals hors de combat.
Party status and the geographical scope of IHL
Identifying who are the parties to an armed conflict matters in establishing the geographical scope of application of IHL. This is particularly the case in IACs, where IHL will generally apply only to the territory of the states that are parties to the conflict. The position in NIACs is more nuanced. It remains unsettled whether IHL applies to the territories of all states that are parties to a NIAC – an issue that arises where foreign states intervene against armed groups extraterritorially alongside the host state. More widely, there is debate on whether the application of IHL within a state party should be confined to acts with a nexus to the conflict, and whether, conversely, IHL could be extended to such acts beyond the territory of a state (the latter both in IACs and in NIACs). However, even if such a nexus approach is accepted, party status would still play a role as part of the assessment of the nexus to the conflict.
Party status and the mandates of humanitarian organizations
Party status may also affect the formal roles and mandates of certain impartial humanitarian organizations in armed conflict. This is notably the case for the ICRC and National Red Cross and National Red Crescent Societies. The ICRC engages with all parties to an armed conflict, particularly to seek compliance with IHL – for example, by reminding them of their obligations. Under the four Geneva Conventions of 1949 and their 1977 Additional Protocol I, parties to a conflict must permit the ICRC to carry out specific humanitarian activities. These include the ICRC’s ability to visit prisoners of war and civilian internees. Accordingly, the ICRC has a particular interest in identifying the parties to an armed conflict.
Moreover, parties to a conflict should grant certain facilities to their respective National Red Cross or Red Crescent Society, the International Federation of Red Cross and Red Crescent Societies and (as far as possible) other humanitarian organizations that are duly authorized by the respective party. This is to enable such organizations to carry out humanitarian activities in favour of the victims of the conflict. These humanitarian activities are further defined in the 1949 Geneva Conventions and Additional Protocol I. Knowing a state’s party status can therefore help humanitarian organizations to understand what roles they may undertake and the related facilities they may expect to receive while working on the territory of that state.
3.3 Party status and international criminal law
Under international criminal law, party status matters in three main ways for establishing whether individuals have committed war crimes.
First, indirectly and at a very basic level, identifying who is a party may matter for establishing whether a specific rule of IHL is violated – so that international criminal responsibility can be attached to a violation. For example, only once a state becomes a party to an IAC do members of their armed forces become lawful targets on the basis of their combatant status under IHL.
Second, at a more specific level, party status also matters for those war crimes – in both international and non-international armed conflict – that presuppose that the perpetrator and/or victim have a specific connection to the parties. Examples include the war crimes of killing or wounding treacherously individuals belonging to the hostile nation or army; destroying or seizing enemy property; declaring abolished the rights of nationals of the hostile party in court; or compelling nationals of the hostile party to take part in the operations of war directed against their own country.
Third, party status plays a role in establishing that a crime has a sufficient nexus to an armed conflict to constitute a war crime. International case law has established the following, non-exhaustive, set of indicators for the nexus assessment: ‘the fact that the perpetrator is a combatant; the fact that the victim is a non-combatant; the fact that the victim is a member of the opposing party; the fact that the act may be said to serve the ultimate goal of a military campaign; and the fact that the crime is committed as part of or in the context of the perpetrator’s official duties.’ All of these indicators entail a connection between the perpetrator, victim or conduct and the parties.
3.4 Party status and IHRL
IHRL continues to bind a state once the state becomes a party to an international or non-international armed conflict. War and peace can no longer be conceived of as entirely separate legal spheres, and becoming a party does not have the effect of freeing a state of its peace time obligations. But the relationship between IHRL and IHL is not entirely settled.
There are some differences in the application of the human rights treaties to parties to armed conflict. Party status may play a role under derogation clauses such as Article 15(2) of the European Convention on Human Rights (ECHR), which permits states not to apply the provision on the right to life with regard to ‘deaths resulting from lawful acts of war’. Moreover, the killing of combatants by a party to a conflict is not generally considered ‘arbitrary’ under Article 6(1) of the International Covenant on Civil and Political Rights (ICCPR) or Article 4(1) of the American Convention on Human Rights (ACHR), if it complies with IHL. The European Court of Human Rights, in Hassan, also interpreted the right to liberty and security under Article 5 ECHR more leniently regarding detention by states that are parties to an IAC. In Georgia v Russia (II), the court even excluded the application of the ECHR altogether ‘in respect of military operations (…) during the active hostilities phase’ of an IAC, although the contours of this scope exclusion remain unsettled, and the court seems more recently to have retreated from this jurisprudence.
3.5 Party status and the law of neutrality
Party status also matters for establishing the rights and duties of third states – that is, those states that are not party to a particular armed conflict. In inter-state conflicts, the legal relationship between third states and states parties to an armed conflict has traditionally been regulated by the law of neutrality. This regime of customary international law is partly codified in the 1907 Hague Conventions V and XIII.
The law of neutrality chiefly requires third states – neutral states – to refrain from certain acts of military assistance to the parties, and to prevent the parties from using neutral territory for waging their war. Conversely, the parties are required to respect the inviolability of neutral territory. The parties have also been said to possess certain ‘belligerent rights’ against neutral states, including searching for and seizing contraband, and establishing blockades. As noted earlier, there is ongoing debate as to how exactly these different elements of neutrality law can apply in light of today’s ius ad bellum. A considerable body of state practice, international judicial decisions, and scholarly literature supports the general notions that the law of neutrality persists to this day, and that it can apply to inter-state conflicts. To the extent that neutrality rules still apply to inter-state conflicts, knowing who is a party to a particular conflict – and, by implication, who is not a party and thus a third state – is crucial in applying these rules.
3.6 Party status and rules on complicity
Beyond neutrality law, in any situation where a state or international organization provides support to another state in the course of an armed conflict, there will be a question of whether the provision of that support is itself lawful. International law imposes what has been referred to as a ‘network of rules on complicity’ on states. There are specific primary rules that prohibit forms of support that do or would facilitate wrongdoing by the recipient state. and there is a general complicity rule set out in Article 16 ASR. Examples of the former include obligations in relation to the trade in arms or weapons and the prohibition on complicity in genocide. The latter is a general rule that prohibits aid or assistance by one state to another that facilitates an internationally wrongful act by the recipient. In general, these rules turn on the commission – or risk of commission – by the assisted state of a wrongful act. In all cases, assisting states will need to undertake a context and rule-specific assessment of their potential responsibility.
In specific circumstances party status may trigger, or affect the scope of, an obligation binding the assisting state.
Complicity rules binding assisting states do not generally themselves turn on whether the assisting state is a party to the conflict. To use the examples above, under Article 6(3) of the Arms Trade Treaty, it does not matter whether the state authorizing the transfer of conventional weapons is a party or not. Similarly, under Article 16 ASR, the assisting state need not be a party for the rule to apply – all that is required is that the assisted state’s act would have been wrongful if it were committed by the assisting state.
Beyond this general statement of principle, in specific circumstances party status may trigger, or affect the scope of, an obligation binding the assisting state. Under Common Article 1 to the Geneva Conventions, states ‘undertake to respect and to ensure respect for the present Convention in all circumstances.’ As to the ‘ensure respect’ limb of the provision, it is generally – if not universally – accepted that all states are bound not to assist or encourage violations of international humanitarian law by other states. Whether or not the assisted state or non-state armed group is a party to the conflict is important, in that most obligations in IHL, which the assisted state could potentially violate, are addressed to the parties. The non-assistance duty in Common Article 1 also applies regarding assistance to a non-state party to an armed conflict. The controversial question of whether the general complicity rule reflected in Article 16 ASR also covers assistance to non-state actors can therefore be left aside.
3.7 Party status and domestic law
Besides the international law implications, being ‘at war’ has traditionally had a wide range of implications in many domestic legal systems – which in some instances refer to international law concepts of party status. Such provisions range from ‘war clauses’ in insurance contracts, to constitutional law arrangements for deploying armed forces abroad, and criminal law offences outlawing treason or terrorist acts. For example, under Danish law it is a criminal offence to enter into the armed forces of an adverse party. Belgian law, meanwhile, excludes acts of the armed forces during armed conflict from the application of terrorist offences.
Whether a particular domestic law provision is to be understood in the light of international law concepts of party status must be considered case-by-case under the relevant domestic law. When a domestic law provision does refer to party status under international law, a state’s understanding of the domestic provision may incidentally also reveal its views on the parallel international law question. For example, if a government is using its constitutional processes for participating in war, this may indicate it considers itself a party to the respective armed conflict as a matter of international law. If the US Congress were to authorize the use of force by statute, or if the US president were to issue reports in compliance with the Wars Powers Resolution, these acts may indicate that the US considers itself a party to an armed conflict under international law, even if the domestic notion of ‘hostilities’ may not be coterminous with the international law concept of party status.
Having sketched out in this chapter how party status, in general, matters to the regulation of armed conflict, the next chapter specifically explores the implications of becoming a co-party.
