Collaborators committed some of the worst atrocities of the Holocaust era. Antisemitism, nationalism, ethnic hatred, anti-communism, and opportunism led many citizens of nations occupied by Germany to collaborate with the Nazi regime in the annihilation of the European Jews.
Germany's Axis partners cooperated with the Nazi regime by enforcing anti-Jewish legislation. In Hungary, Slovakia, Croatia, Bulgaria, and Vichy France, local police, military, and other officials were vital to the deportation of Jews to the German killing centers in the East. In some Axis states, fascist paramilitary organizations terrorized, robbed, and murdered indigenous Jews, either under German guidance or on their own initiative. The Hlinka Guard in Slovakia, the Iron Guard in Romania, the Ustasa in Croatia, and the Arrow Cross in Hungary were responsible for the deaths of thousands of Jews in their home territory.
Throughout eastern and southeastern Europe, many local people served as guards in Nazi camps and were involved in the murder by poison gas of hundreds of thousands of Jews. Lithuanians, Latvians, Estonians, Belorussians, and Ukrainians spontaneously formed groups which killed hundreds of Jews as well others suspected of being Communists. The Germans reorganized these units into ruthless police auxiliaries that assisted in the massacre of hundreds of thousands of Jews and millions of non-Jews in the occupied Soviet Union. Throughout the period of the occupation, the Germans continued to recruit auxiliaries for their police forces, military units, and civilian administrations from among the native peoples of the Soviet Union.
The government of Vichy France cooperated with the Germans by legally defining Jews by race and restricting their rights. Vichy authorities established internment camps in southern France and aided in the deportation of Jews to killing centers in German-occupied Poland. After the German invasion of Norway, Vidkun Quisling, a Norwegian fascist, proclaimed himself prime minister. The Germans quickly became disillusioned with him, but Quisling's name entered the English dictionary as the definition of a collaborationist traitor. In Belgium and the Netherlands, local civilian and police authorities collaborated closely with the Germans in rounding up and deporting Jews to killing centers.