Offenses prosecutable under international humanitarian law and international criminal law for atrocities committed in armed conflict or as part of a widespread or systematic attack on a civilian population, together with the discipline's own recognized scholarly vocabulary for describing mass atrocity that falls outside or alongside these offenses' own narrow legal definitions. This group gathers the four core international crimes (genocide, war crimes, crimes against humanity and the crime of aggression) and their specific prohibited methods and conduct under the Rome Statute and the Geneva Conventions, including torture, persecution, extermination, ethnic cleansing, enforced disappearance, pillaging, perfidy, the use of chemical, biological, incendiary and blinding-laser weapons, anti-personnel landmines and cluster munitions, the recruitment of child soldiers, attacks on humanitarian personnel, destruction of cultural property, collective punishment and the denial of quarter to a surrendering enemy, alongside the scholarly typologies (democide, politicide, gendercide, classicide, cultural genocide) that name comparable government-perpetrated mass harm the Genocide Convention's own definition does not reach. It excludes offenses against a state's own internal political authority rather than against humanity or the laws of war, which belong under Treason, Sedition and Offenses Against the State, and excludes the recruitment and financing offenses of terrorism and mercenary warfare specifically, which belong under Terrorism Offenses and this group only when the international instrument itself frames mercenary recruitment as a war-crime-adjacent international offense rather than a domestic terrorism statute.