 The Winter War ( Finnish : Talvisota , Swedish : Vinterkriget , Russian : Зи ́ мняя война ́ , tr . Zimnyaya voyna ) was a military conflict between the Soviet Union and Finland in 1939 – 1940 . It began with the Soviet invasion of Finland on 30 November 1939 ( three months after the outbreak of World War II ) , and ended with the Moscow Peace Treaty on 13 March 1940 . The League of Nations deemed the attack illegal and expelled the Soviet Union from the League on 14 December 1939 . 
