Equality of belligerents between States and armed groups: Proposal for a new definition of the principle of equality in non-international armed conflicts

The principle of equality of belligerents mandates that the rules of international humanitarian law (IHL) apply equally to each party in an armed conflict, regardless of the legality of their use of force under jus ad bellum. This principle has been extensively analyzed in academic literature; its importance is universally recognized and its legal foundations and effects are well defined. However, this is primarily true with respect to its application in international armed conflicts (IACs) - in contrast, the principle does not receive equivalent recognition in situations of non-international armed conflict (NIAC), where at least one party is a non-State armed group. The issue arises from the lack of an accepted definition of the principle in NIACs, given the absence of any applicable international jus ad bellum in such conflicts. The present paper will try to remedy this issue by proposing that the principle is composed of two elements: symmetry of application and symmetry of substance. It will introduce this definition as it applies to IACs and NIACs and argue that the principle in NIACs is primarily defined by its symmetry of substance component. It will also evaluate the principle's nature as a general principle of IHL and explore some of its concrete effects on IHL rules.