After World War II the United Nations Convention on the Prevention and Punishment of the Crime of Genocide was approved by the United Nations in 1948 and adopted by the international community. It defines Genocide, inter alia, as: "The killing or causing of serious bodily or mental harm to members of a national, ethnic, racial or religious group in whole or in part".
Its intention was to protect a civilian population. It also gave rise to a concept previously elucidated at the Nuremberg Tribunal (1946), that of a crime against humanity.
The Genocide Convention intended to cover Hitler's policy of exterminating German Jews, who were German citizens. The Convention made sure that if ever something like that happened again, it would no longer be considered an internal matter, but a matter subject to international law.