Stalin, who was the leader of the Soviet Union, did not like having a capitalist country as its neighbour. Stalin wanted Finland to become a communist state and be a part of the Soviet Union. The leaders of Finland refused: they wanted to stay independent. The Soviet Union sent many troops across the eastern border of Finland to try to make Finland join them, which resulted in the Winter War. The Soviet Union eventually won, and took most of Karelia and other parts of Finland.