By late March 1941, Bulgaria and Yugoslavia signed the Tripartite Pact; however, the Yugoslav government was overthrown two days later by pro-British nationalists. Germany responded with simultaneous invasions of both Yugoslavia and Greece, commencing on 6 April 1941; both nations were forced to surrender within the month. The airborne invasion of the Greek island of Crete at the end of May completed the German conquest of the Balkans. Although the Axis victory was swift, bitter and large-scale partisan warfare subsequently broke out against the Axis occupation of Yugoslavia, which continued until the end of the war.