Outnumbered four to one, Finland held off the Soviet invasion for months

When the Soviet Union invaded Finland in November 1939, Stalin expected victory within weeks. Finnish troops, fighting on skis in white camouflage in temperatures as low as -40°C, inflicted disproportionate losses on the much larger Red Army for over three months. Finland eventually ceded territory in the peace treaty but kept its independence, and the war exposed serious weaknesses in the Soviet military.

— Wikipedia contributors, Winter War — Soviet invasion of Finland, 1939-1940