1939 Soviet Invasion of Finland
In 1938, the Soviet Union began planning for the likelihood of a war with Germany. They contacted Finland about ceding border lands which they felt were vulnerable to attack, but Finland refused. On October 5, 1939, the Soviet Union gave Finland one final offer, the border between Finland and the USSR on the Karelian Isthmus would be moved 30km west and all Finnish fortifications on the border would be destroyed. They also demanded the islands in the Gulf of Finland and Kalastajansaarento Peninsula. Finally, the wanted to lease the Hanko Peninsula for 30 years. In return, the Soviet Union offered two municipalities which had twice the land that the USSR was requesting.
After much debate the Finnish government rejected the offer. On November 30, 1939, the USSR invaded Finland with 450,0000 men. They also began bombing Helsinki. There was no declaration of war, and the act violated several non-aggression pacts. The League of Nations condemned the action and expelled the Soviet Union. The Soviet Union believed that they could easily defeat Finland in a matter of weeks, and some reports suggest that they intended to conquer the entire country.
However, Finland fought back despite being outnumbered and at a disadvantage militarily. The Soviets experienced large numbers of casualties and were thoroughly embarrassed by the end of the first month of the war. Help from the League of Nations never came as Norway and Sweden refused to allow troops passage to Finland.
On March 12, 1940, the 105-day war ended with Finland making an offer to the Soviet Union. They would meet all the demands of the USSR on October 5, in addition they surrendered the entire Karelian Isthmus and a large piece of land north of Lake Ladoga. Part of the Salla region was also ceded to the Soviets. 12% of Finland’s population were evacuated from their homes in order to remain in Finnish territory. The Soviets got everything they wanted without ceding any territory, but they did experience large numbers of casualties during the war.