Who is at War? On the Question of Co-belligerency

When does a state, by assisting one of the parties to an international armed conflict (IAC), become a party to it? Although the doctrinal answer to this question is somewhat unsettled, this chapter does not dispute or defend a specific doctrinal view. Instead, it explores the tension between philosophical accounts of the ethics of war and international humanitarian law (IHL), as it arises in the context of co-belligerency. After canvassing different doctrinal answers, the chapter discusses McMahan’s and similar revisionist views and to what extent they conflict with IHL’s positive answer to the question of co-belligerency. Then, the chapter argues that the ‘humanitarian view’ can partially solve this conflict, but it is still open to an important objection concerning IHL’s ability to reduce suffering, particularly in the long term. In order to dispel this objection in a morally attractive way, we have to concede that sometimes IHL reduces suffering at the expense of the rights of the innocent. This concession, the chapter argues, raises overarching concerns about IHL’s moral coherence and standing.