Any of various crimes, such as genocide or the mistreatment of prisoners of war, committed during a war and considered in violation of the conventions of warfare.war criminal n. a cruel act done during a war which is illegal under international law. Any violation of the laws of war, as laid down by international customary law and certain international treaties. At the end of World War II, the part of the London Agreement signed by the U.S., Britain, the Soviet Union, and France established three categories of war crime: conventional war crimes (including murder, ill treatment, or deportation of the civilian population of occupied territories), crimes against peace, and crimes against humanity (political, racial, or religious persecution against any civilian population). The charter also provided for an international military tribunal to try major Axis war criminals. It further stated that a defendant's position as head of state would not free him from accountability, nor would having acted on orders or out of military necessity. German and Japanese war criminals were tried before Allied tribunals in Nürnberg and Tokyo in 1945-46 and 1946-48, respectively, and in the 1990s tribunals were created for the prosecution of war crimes committed in Rwanda and the territory of the former Yugoslavia. See also Geneva Convention; genocide; Hague Convention; Nürnberg trial