The Holocaust describes the killing of approximately six million European Jews during World War II executed by the National Socialist regime in Germany led by Adolf Hitler. Other groups persecuted and killed by the regime were the Roma, Soviet POWs, disabled people, gay men, Jehovah's Witnesses, Roman Catholic Poles, and political prisoners. The persecution and genocide were accomplished in stages. Legislation to remove the Jews from civil society was enacted. Ghettos, concentration camps, extermination camps and gas chambers were established. Specialized units called Einsatzgruppen murdered Jews and political opponents in mass shootings. [Picture: Holocaust Memorial, Miami, Florida]