Within nations occupied by the Axis Powers in World War II, some citizens and organizations, prompted by nationalism, ethnic hatred, anti-communism, antisemitism, opportunism, self-defense, or often a combination, knowingly collaborated with the Axis Powers. Some of these collaborators committed war crimes, crimes against humanity, or atrocities of the Jewish Holocaust.
Collaboration has been defined as cooperation between elements of the population of a defeated state and representatives of a victorious power.Stanley Hoffmann subdivided collaboration into involuntary (reluctant recognition of necessity) and voluntary (exploitation of necessity). According to Hoffmann, collaborationism can be subdivided into "servile" and "ideological"; the former is deliberate service to an enemy, whereas the latter is deliberate advocacy of cooperation with a foreign force which is seen as a champion of desirable domestic transformations. In contrast, Bertram Gordon uses the terms "collaborator" and "collaborationist", respectively, in reference to non-ideological and ideological collaborations.
The term "collaborator" has also been applied to persons, organizations, or countries that were not under occupation by the Axis Powers but that ideologically, financially, or militarily, before or during World War II, supported Nazi Germany, Fascist Italy, or World War II-era Imperial Japan.
After the Italian invasion of Albania, the Royal Albanian Army, police and gendarmerie were amalgamated into the Italian armed forces. A fascist Albanian Militia was also formed and in the Yugoslav part of Kosovo they established Vulnetari (or Kosovars) a volunteer militia of Albanians from Kosovo. Ethnic Albanian elements of the Italian armed forces participated in the Italian invasion of Greece, and German-led Axis invasion of Yugoslavia. After the capitulation of Italy, the Germans stepped in and established more collaborationist units such as police volunteer regiments and a national militia. In annexed Kosovo, the Germans established the Kosovo Regiment out of Balli Kombëtar forces. In April 1943, Reichsfuhrer-SS Heinrich Himmler created the 21st Waffen Mountain Division of the SS Skanderbeg (1st Albanian) manned by Albanians and Kosovar Albanians. By June 1944, its military value against the Albanian and Yugoslav Partisans was considered poor, and by November 1944 it had been disbanded. The remaining cadre, now called Kampfgruppe Skanderbeg, was transferred to the Prinz Eugen Division where they successfully participated in actions against Josip Broz Tito's partisans in December 1944. The emblem of the division was a black Albanian eagle.