The Holocaust, also referred to as the Shoah, was a genocide during World War II in which Adolf Hitler's Nazi Germany, aided by its collaborators, systematically murdered some six 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 involving the persecution and murder of other groups, including in particular the Roma and "incurably sick", as well as political opponents, gay men, Jehovah's Witnesses, ethnic Poles and Soviet prisoners of war.
Germany implemented the persecution in stages. Following 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.