One of the earliest references to a crime against humanity in modern times was made with regard to slavery in a speech delivered in the United States in 1872. The massacre of Armenian people in Turkey was described by a 1915 joint resolution of France, Great Britain, and Russia as representing crimes against humanity (although by the early 2000s the term "genocide" was more commonly applied to the Armenian massacre). After World War I (1914–1918), most of the victorious powers wanted to create a war crimes tribunal to prosecute German leaders under universal principles of justice, but the United States opposed that idea. As a result, by far the most important conceptualization of crimes against humanity came after World War II (1939–1945) in the Nuremberg Principles, which were applied to Hitler's Third Reich.

The Treaty of London of August 8, 1945, provided for the creation of the International Military Tribunal...