The Holocaust happened primarily in German-occupied Europe during World War II, from 1933 to 1945. It began in Germany after Adolf Hitler became chancellor in 1933 and expanded as Nazi Germany annexed, invaded, and occupied neighboring countries. Major sites of the Holocaust included Nazi Germany, occupied Poland, and other territories controlled by the Axis powers. The genocide was carried out in ghettos, concentration camps, and specially designed killing centers (extermination camps) such as Auschwitz-Birkenau, Chelmno, Belzec, Sobibor, and Treblinka, mostly located in occupied Poland. The Nazi regime and its collaborators systematically persecuted and murdered six million Jews across much of Europe during this period.