the nation's extreme political movements had diminished. After Soviet involvement in the Finnish Civil War in 1918, no formal peace treaty was signed. In 1918 and 1919, Finnish volunteers conducted two unsuccessful military incursions across the Soviet border, the Viena and Aunus expeditions, to annex areas in Karelia that according to the Greater Finland ideology would combine all Baltic Finnic peoples into a single state. In 1920, Finnish communists, based in Soviet Russia, attempted to assassinate the former Finnish White Guard Commander-in-Chief, Marshal Carl Gustaf Emil Mannerheim. On 14 October 1920, Finland and Soviet Russia signed the Treaty of Tartu, confirming the old border between the autonomous Grand Duchy of Finland and Imperial Russia proper as the new Finnish–Soviet border. Finland also received Petsamo Province, with its ice-free harbour on the Arctic Ocean. Despite the signing of the treaty, relations between the two countries remained strained. The Finnish government allowed volunteers to cross the border to support the East Karelian uprising in Russia in 1921, and Finnish communists in the Soviet Union continued to prepare for revenge and staged a cross-border raid into Finland, the Pork Mutiny, in 1922. In 1932, the Soviet–Finnish Non-Aggression Pact was signed between both countries, and it was reaffirmed for ten years in 1934. Foreign trade in Finland was booming, but less than 1% of it was with the Soviet Union. In 1934, the Soviet Union also joined the League of Nations. Justification Soviet General Secretary Joseph Stalin regarded it a disappointment that the Soviet Union could not halt the Finnish Revolution. He thought that the pro-Finland movement in Karelia posed a direct threat to Leningrad and that the area and defences of Finland could be used to invade the Soviet Union or restrict fleet movements. Soviet propaganda then painted Finland's leadership as a "vicious and reactionary fascist clique". Field Marshal Mannerheim and Väinö Tanner, the leader of the Finnish Social Democratic Party, were targeted for particular scorn. When Stalin gained absolute power through the Great Purge of 1938, the Soviets changed their foreign policy toward Finland and began to pursue the reconquest of the provinces of Tsarist Russia that had been lost during the chaos of the October Revolution of 1917 and the Russian Civil War almost two decades earlier. Soviet leaders believed that the old empire's extended borders provided territorial security and wanted Leningrad, only from the Finnish border, to enjoy a similar