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.
(Though the border that was "only 32 km (20 mi)" from Leningrad was the end of a narrow finger of coastline about 15 km (9.3 mi) long by 5 km (3.1 mi) wide; most of the Finnish border was more than 50 km (31 mi) from Leningrad.) Finland refused and the USSR invaded the country.
Many sources conclude that the Soviet Union had intended to conquer all of Finland, and use the establishment of the puppet Finnish Communist government and the Molotov–Ribbentrop Pact's secret protocols as proof of this, The Soviets possessed more than three times as many soldiers as the Finns, thirty times as many aircraft, and a hundred times as many tanks.
The Red Army, however, had been crippled by Soviet leader Joseph Stalin's Great Purge of 1937.
However, after reorganization and adoption of different tactics, the renewed Soviet offensive overcame Finnish defenses at the borders.
Finland then agreed to cede more territory than originally demanded by the Soviet Union in 1939; the Soviets, having conquered the areas they demanded from Finland but at a cost of heavier losses in troops than anticipated, accepted this offer.
While the Soviet Union did not conquer all Finland, Soviet gains exceeded their pre-war demands.
They gained substantial territory along Lake Ladoga, providing a buffer for Leningrad, and territory in northern Finland.
Finland retained its sovereignty and enhanced its international reputation.
The end of the war cancelled the Franco-British plan to send troops to Finland through northern Scandinavia.
Some authors would suggest that the official statement by Sweden, Norway and Denmark of February 1940, declaring they would not allow British troops to use their territories on their way to Finland, was a factor in Finland's decision of starting peace talks with Russia.
Until the beginning of the 19th century, Finland constituted the eastern part of the Kingdom of Sweden.