The Holocaust was the systematic persecution and murder of approximately six million Jews by the Nazi regime and its collaborators between 1933 and 1945. Adolf Hitler was the leader behind ordering the genocide. Anti-Semitism, or discrimination against Jews, was a major factor that enabled the Holocaust. After World War II, neo-Nazism emerged, consisting of groups seeking to revive Nazi ideology, including Holocaust denial. The Nazis established ghettos in Poland and Eastern Europe to segregate Jewish communities, the largest being in Warsaw, and deported thousands daily to concentration camps like Auschwitz.