In 1920, Finnish communists based in the USSR attempted to assassinate the former Finnish White Guard Commander-in-Chief, Marshal Carl Gustaf Emil Mannerheim.
Hostilities ceased in March 1940 with the signing of the Moscow Peace Treaty.
Finland ceded territory representing 11 percent of its land area and 13 percent of its economy to the Soviet Union.
Field Marshal Mannerheim and Väinö Tanner, the leader of the Finnish Social Democratic Party, were targeted for particular scorn.
With Stalin gaining absolute power through the Great Purge of 1938, the USSR changed its foreign policy toward Finland in the late 1930s and began pursuing the reconquest of the provinces of Tsarist Russia lost during the chaos of the October Revolution and the Russian Civil War almost two decades earlier.
Yartsev suggested that Finland cede or lease some islands in the Gulf of Finland along the seaward approaches to Leningrad; Finland refused.
Negotiations continued throughout 1938 without results. Finnish reception of Soviet entreaties was decidedly cool, as the violent collectivization and purges in Stalin's Soviet Union resulted in a poor opinion of the country.Soviet leadership believed that the old empire possessed ideal the amount of territorial security, and wanted the newly-christened city of Leningrad to enjoy a similar level of security; in essence, the border between Finland and Russia was never supposed to become international.In April 1938, NKVD agent Boris Yartsev contacted the Finnish Foreign Minister Rudolf Holsti and Prime Minister Aimo Cajander, stating that the Soviet Union did not trust Germany and that war was considered possible between the two countries.The Red Army, however, had been crippled by Soviet leader Joseph Stalin's Great Purge of 1936–1938.However, after reorganization and adoption of different tactics, the renewed Soviet offensive overcame Finnish defences at the borders.The Communist Party of Finland was declared illegal in 1931, and the nationalist Lapua Movement organised anti-communist violence, which culminated in a failed coup attempt in 1932.