The expansive politics of Germany led Europe into crises in the end of 1930's. The multifold political and military events culminated in August 1939 in the nonaggression pact between Hitler's Germany and Stalin's Soviet Union including the secret protocol placing Finland into the Soviet sphere of influence.
In the fall of 1939 the Soviet Union began to strengthen its position by acquiring bases in the Baltic states and demanding territorial concessions from Finland in order to improve the security of Leningrad. The negotiations broke down without results and on 30.11.1939 the armed forces of the Soviet Union crossed the Finnish borders in many places. The Winter War had started.
In the ensuing 105 days of fighting the poorely equipped but well trained field army of Finland repelled the attacks of numerically superior Soviet troops in Ladoga Karelia and northern Finland.
However, in the great offensive launched in mid-February 1940 the enemy succeeded in breaking the main defensive line, the Mannerheim-line, in the Karelian Isthmus and the defenders withdrew to Viipuri-Vuoksi line.
Finland had to fight in extremely harsh conditions almost alone. The nation was nearly exhausted when negotiations at a political level were successfully initiated and resulted finally in the signing of the Moscow peace treaty 13.3.1940. According to the treaty Finland had to relinguish south-eastern Finland, parts of Salla and Petsamo and to lease the Hanko-area.
Almost 25 000 men and women were killed either in action or in home front, 45 000 were wounded.