How to Cope with Diversity While Preserving Unity in Customary International Law? Some Insights from International Humanitarian Law

Drawing upon literature relating to armed groups and international law, this article provides insights on the question of whether customary international law can accommodate non-state actors at the level of duty-bearers and norm-makers. Demonstrating that customary international law can accommodate considerable diversity at the level of duty-bearers, it argues that customary international law will struggle to accommodate diversity at the level of its makers. In particular, it points out that the character of armed groups is so different from that of states, that it is unclear how their practice could be taken into account alongside those of states. Yet, the article demonstrates that there are also problems in a methodology relying upon only state practice and opinio juris, as evidence of customary norms binding on a diversity of actors. It shows that this is particularly the case for human rights law, where the identity of the norm-making entity ‘as a state’ is highly determinative of the nature of its practice and opinio juris.