In Enemies of Mankind Walter Rech offers a contextual history of the collective security doctrine articulated by Swiss international lawyer Emer de Vattel (1714-67) in the authoritative treatise Droit des gens of 1758. With reference to Vattel’s writings and to early modern international history and legal thought more generally, Rech explores the meanings and functions of the enemy of mankind concept and its ramifications for collective security. This account complicates the canonical portrayal of Vattel as an advocate of state sovereignty and a critic of law enforcement in the international society, thus reappraising his place in the history of international law.