The Holocaust, also referred to as the Shoah, was a genocide in which some six million European Jews were killed by Adolf Hitler's Nazi Germany, and the World War II collaborators with the Nazis. The victims included 1.5 million children, and represented about two-thirds of the nine million Jews who had resided in Europe. A broader definition of the Holocaust includes non-Jewish victims of the Nazi campaign of mass murder, based on biological factors, such as the Romani, and the Aktion T4 patients who were mentally and physically disabled
