Analysing the development of the concept of non-state parties to an armed conflict from the writings of philosophers in the eighteenth century through international humanitarian law (IHL) treaty law to contemporary practice, three threads can be identified. First, as pointed out by Rousseau almost two and a half centuries ago, one basic principle underlying the laws of war is that war is not a relation between men but between entities. Accordingly, the lawful objective of parties cannot be to harm opponents as individuals but only to overcome the entity for which the individual fights. This necessitates that any party to an armed conflict is a collective, organized entity and not a loosely connected group of individuals. Second, de Vattel already stressed that civil war is fought between two parties who ‘acknowledge no common judge’ and have no ‘common superior’ on earth....
