Finnish Soldiers during the Winter War using a slingshot to lob grenades at the Soviets. The Winter War began with the Soviet invasion of Finland on 30 November 1939. This attack was considered illegal for The League of Nations and therefore, the Soviet Union was expelled from the League. The Soviet Union, which had before claimed sovereignty on some areas of Finnish territory, demanded concessions of several lands in the Leningrad area claiming security reasons. Finland refused and the USSR invaded the country. Numerically superior, the Soviets, though the whole invasion of Finland would be an easy job. Nevertheless, the Finnish forces repelled Soviet attacks for several months, far much longer than the Soviets expected. Hostilities ceased in March 1940 with the signing of the Moscow Peace Treaty, as the Red Army had been gaining land and Finland ceded territory representing 11% of its land area and 13% of its economy. The poor performance of the Red Army encouraged Hitler to think that an attack on the Soviet Union would be successful and reconfirmed negative Western opinions of Soviet military. 25,904 Finnish soldiers perished in the war, in front of c. 140,000 Soviets.