From treaty to custom: Shifting paths in the recent development of international humanitarian law

From 1864 to the 1970s, international humanitarian law (IHL) changed through the path of formal treaty revision. Since 1977, however, purported changes to IHL have come not from treaty making but from interpretation, particularly through claims about the attainment of customary status by existing treaty rules. This article explains this shift as the result of the attitudes and choices of key IHL stakeholders under the changed conditions of post-Second World War multilateralism. It argues that the turn toward customary law claims-making was a reaction to the negotiation politics and contested outcomes of the 1977 Additional Protocols (APs) to the Geneva Conventions. After 1977, leading actors looked to custom as a means of arresting or encouraging legal change. The resulting, much-expanded IHL has proved influential and authoritative, even if its precise degree of acceptance by states remains unclear.