World War II in Finland began on 30 November 1939 when the Soviet Union invaded, starting the Winter War. Fighting between the two lasted for a few months until Finland gave away territory to the USSR. On 22 June 1941, Finland allied with Nazi Germany (but not officially an Axis member) in Operation Barbarossa (the German invasion of the USSR), starting the Continuation War. Finland participated in the Siege of Leningrad on the northern front of the Siege. In 1944 the Finnish forces were pushed back away from Leningrad. Finland signed a peace treaty with the USSR and left the war against the Soviet Union. But the German forces in Lapland refused to leave, starting the Lapland War. The Finish forces and the Red Army pushed the Germans back to Norway. Finland was fully liberated on 27 April 1945, ending Finland's participation in the war. In the end, Finland gave up 10% of its territory to the Soviet Union for its role in the Continuation War.