After the Italian invasion of Albania, and the commencing of the Greco-Italian War, many Albanians voluntarily joined the war. Among the first were Musliu, Xhem and Abdullah. The three brothers fought in the Battle of Greece in 1941. [After the fall of Greece and Yugoslavia in April 1941, Hasa returned to Gostivar, where he gathered local Albanians to form a group of fighters who occupied Gostivar. In the autumn of 1943, Germany occupied all of Albania after Italy was capitulated. The Balli Kombëtar made a deal with the Germans and formed a collaborationist government in Tirana which continued its war with the LNC and Yugoslav Partisans. Xhem Hasa and his battalion was incorporated into the Balli Kombëtar. Hasa's victories in battles led to his elevation as the commander of the Balli Kombëtar in Macedonia.