This chapter elaborates on specific implications of party status for co-parties to armed conflict.
Becoming a co-party to an armed conflict can have significant political implications. This is particularly true in IACs, due to the significant symbolic weight associated with being ‘at war’, and the escalatory potential of such a signal both to other states and to domestic audiences. States may, therefore, have legitimate political reasons to avoid actions that would make them a co-party. In setting this red line for their conduct, however, states should be clear that choosing to abstain from certain actions to avoid becoming a co-party is itself a political choice.
There can be a risk of portraying a distorted image of international law on this point. Becoming a co-party is not, in and of itself, a violation of international law. As discussed previously, whether the acts of a state that becomes a co-party are lawful depends chiefly on their compliance with applicable rules of international law, including, first and foremost, the ius ad bellum and ius in bello. As regards the former, this means that the acts, if they amount to a use of force, must be authorized by the UNSC or, more likely, be justified in individual or collective self-defence. Co-party status, by contrast, is about which rules apply to the conduct of a state, international organization or non-state party, to their relationship with third states and to individuals connected to the co-party.
In addition to communicating accurately the political nature of their perceived constraints, it is crucial that states, international organizations, and non-state armed groups base their course of action on an accurate understanding of what becoming a co-party means as a matter of international law. The actual legal implications may be relevant to the political calculus and must, in any event, be carefully considered so as to enable the correct application of – and compliance with – international law.
As a general matter, being a co-party has all the legal implications of being a party to an armed conflict, as set out in Chapter 3. Factual circumstances will determine which of these many legal implications of party status will be most relevant to a particular co-party in a given conflict. Co-parties will have to consider how their obligations apply in cooperation contexts. For example, in situations where multiple co-parties contribute to a coordinated attack, a state must consider the whole of the attack when making the proportionality assessment for targeting purposes, not simply its own contribution. These multiple contributions will have to be considered in assessing whether the expected civilian harm is excessive in relation to the anticipated military advantage of the ‘attack as a whole’.
Importantly, co-party status for a single co-party also has significant legal implications for the relationship between multiple co-parties. Specifically, co-parties have obligations flowing from their party status regarding how their fellow co-parties behave in an armed conflict. There are many specific obligations in IHL treaties and customary international law addressed to the parties to an armed conflict, which, for co-parties, can be understood as requiring positive steps in regard to fellow co-parties in the conflict. This does not entail adding further obligations for co-parties. Instead, it flows from interpreting and applying to co-parties the general obligations addressed to all parties to an armed conflict.
Consider, for example, the obligation of parties to take ‘constant care’ in the conduct of military operations to spare civilians. ‘Constant care’, like other precautions, should be understood as requiring such measures as are ‘feasible’. For co-parties, doing what is ‘feasible’ includes taking steps to ensure that partners also spare civilians in the conduct of military operations. This obligation only applies, however, to those military operations in the conduct of which the respective co-party has some involvement. That is, the obligation will be particularly relevant to military operations coordinated between multiple co-parties. The extent to which action is ‘feasible’ regarding fellow co-parties depends on a range of circumstantial factors, including the degree of coordination and the degree of influence of a given party over the specific military operations. In practical terms, relevant measures may include providing expertise, technological means or intelligence (e.g. on the location of civilian objects) for implementing target selection and verification processes that build in sufficient precaution to spare civilians.
In the aftermath of military operations, the duty to investigate may comprise investigations into potential IHL violations of one’s fellow co-parties. Particularly where one co-party is not in a position to investigate on its own (for example, due to a lack of expertise, technological means or other resources), assistance by fellow co-parties becomes relevant – for example, by way of cooperating in gathering information. In such a case, the co-party that requires assistance is under an obligation to request such assistance (if feasible), and the co-party that is able to assist is under an obligation to provide the assistance (to the extent that this is feasible).
In addition to these ‘active’ precautions, ‘passive’ precautions – as a defending party – may, for co-parties, also include assisting one’s partners in removing their civilian nationals from the vicinity of military objectives. In this way, passive precautions can also become relevant to co-parties operating extraterritorially, without their own civilian nationals being at risk through military operations by the adversary.
A co-party’s positive obligation to take all ‘possible’ measures to search for, collect and care for missing, wounded, sick and dead individuals includes assisting fellow co-parties in providing for such protection, and, conversely, requesting such assistance if needed.
There are also positive duties regarding fellow co-parties in the realm of protecting individuals affected by armed conflict. A co-party’s positive obligation to take all ‘possible’ measures to search for, collect and care for missing, wounded, sick and dead individuals includes assisting fellow co-parties in providing for such protection, and, conversely, requesting such assistance if needed. This is because the positive duties of parties to provide for protection apply to all protected individuals, irrespective of who has, for example, injured the respective individuals. What measures are ‘possible’, again, depends on the circumstances. Appropriate measures for co-parties to fulfil their obligations in this respect may include, for example, providing medical facilities, personnel, and other resources either to ensure adequate medical treatment or to facilitate the identification of missing and dead persons by gathering and sharing information.
Beyond specific obligations addressed to parties, the general duty under Common Article 1 to the Geneva Conventions to ‘ensure respect’ for IHL may entail positive obligations of relevance to co-parties. It is controversial whether all states have a positive obligation, under Common Article 1 to the Geneva Conventions, to ensure respect for IHL by the parties to an armed conflict. There is a good case, however, that co-parties at least bear such an obligation with regard to their fellow co-parties. For co-parties, such an obligation would be in line with their primary responsibility – as parties to a conflict – to ensure that the conflict is carried out in accordance with IHL.
As previously discussed, military operations between multiple partners must be closely coordinated for states, international organizations or armed groups to become co-parties. This close coordination must then also be used to fulfil positive duties of protection imposed on parties. Co-parties must cooperate to fulfil their protection obligations. In short, co-party status is about protection through cooperation. The demands placed on co-parties by international law in this regard are not unrealistic. Unlike co-parties’ negative obligations to refrain from certain actions – which constitute absolute prohibitions of actions such as attacking undefended localities – co-parties’ positive obligations are limited to what can be ‘feasibly’ or ‘possibly’ expected. To meet these standards, co-parties must exercise due diligence, but they are not bound to secure a specific result. This is true of the specific positive obligations of co-parties in the realms of the conduct of hostilities and the protection of persons, just as for the positive obligation under Common Article 1 to ensure respect for IHL by fellow co-parties.
The positive duties of co-parties thus are sufficiently flexible to account for the specific operational realities that states may face in a given conflict. For example, how far parties are required to go to fulfil their positive duties to take precautions depends, among other things, on the extent to which a co-party is involved in the conduct of the relevant part of the hostilities. The further co-parties operating in coalitions have intertwined their command-and-control structures, the greater a co-party’s influence on the conduct of hostilities by its fellow co-parties will be – and the more precautions will be feasible. This consideration may, for example, be relevant in situations of multinational operations where states may delegate operational command and control to others. Turning to an example in the realm of the protection of individuals, the reach of the obligations to care for protected persons will depend on what personnel or technical resources of protection a co-party has available – or can make available.
In addition to the legal implications that follow specifically from being a co-party, the factual context of cooperation in military operations may also give rise to responsibility for aiding and assisting violations of international law committed by partners – be it under general complicity rules, IHRL or domestic law. As stated in Section 2.6, such responsibility does not necessarily attach to being a (co-)party, although this and other possible wider implications of cooperation in armed conflict should be kept in mind.
