Within nations occupied by the Axis Powers, some citizens, driven by nationalism, ethnic hatred, anti-Communism, anti-Semitism, or opportunism knowingly engaged in collaboration with the Axis Powers during World War II. These collaborationists committed some of the worst war crimes, crimes against humanity and atrocities of the Holocaust.
Collaboration is "a co-operation between elements of the population of a defeated state and the representatives of the victorious power".Stanley Hoffmann subdivided collaboration into involuntary (reluctant recognition of necessity) and voluntary (exploiting necessity). According to him, collaborationism can be subdivided into "servile" and "ideological"; the former is a deliberate service to an enemy, whereas the latter is a deliberate advocacy of co-operation with the foreign force which is seen as a champion of some desirable domestic transformations. In contrast, Bertram Gordon used the terms "collaborator" and "collaborationist" for non-ideological and ideological collaborations, respectively.
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.