Abstract The history of the notion of “war crimes” spans at least ten centuries. As far as the Western hemisphere is concerned, it starts some time in the twelfth and thirteenth centuries, absorbs normative content during the following centuries, appears as a phrase in the eighteenth century, takes juridical shape and becomes an accepted notion in the nineteenth century, and starts being enforced as a category of criminalized violations of the laws of war with greater regularity in the late nineteenth and twentieth centuries. Today, war crimes constitute one of the “core” categories of recognized international crimes. During that long process of normative development, a core set of rules and prohibitions crystallized to form a body of law first referred to as the laws and customs of war and later as international humanitarian law (IHL) when those laws and customs came to be accepted as truly international. Various means of enforcement – reprisals, hostage-taking, reparations – would be tried over time to give this body of law and its prohibitions a degree of coercive power and deterrence. Slowly, the idea that individual criminal responsibility should attach to the violation of some of the most important prohibitions of IHL came to be accepted as an alternative to what had proven to be ineffective means of enforcement. The notion of “war crimes” grew out of this process, and the list of conduct coming under that umbrella expanded significantly during the nineteenth and twentieth centuries under the combined pressures of violent historical events and the prosecutorial and codificatory efforts that resulted from those events. The twentieth century witnessed the general acceptance of the notion of war crimes, their recognition as norms of customary international law, their frequent domestic and international enforcement, the refinement of their legal contours, their expansion into new territories including non-international armed conflicts, and the creation of institutions, jurisdictional principles and mechanisms geared towards the effective enforcement of those offences and prohibitions.
Guénaël Mettraux (Tue,) studied this question.