The Holocaust, also referred to as the Shoah, was a genocide during World War II in which Nazi Germany, aided by its collaborators, systematically murdered approximately 6 million European Jews, around two-thirds of the Jewish population of Europe, between 1941 and 1945. Jews were targeted for extermination as part of a larger event which involved the persecution and murder of other groups by the regime, including in particular the Roma, and "incurably sick", as well as homosexuals, political opponents, Jehovah's Witnesses, Soviet prisoners of war, and Slavs.
Germany implemented the persecution in stages. Following Adolf Hitler's rise to power in 1933, the government passed laws to exclude Jews from civil society, most prominently the Nuremberg Laws in 1935. Starting in 1933, the Nazis built a network of concentration camps in Germany for political opponents and people deemed "undesirable". After the invasion of Poland in 1939, the regime set up ghettos to segregate Jews. Over 42,000 camps, ghettos, and other detention sites were established.