In 1946, the united nations and the western allies forced the soviet union to withdraw from

The United States and other Western powers wanted to remove Soviet occupations from Eastern Europe where they took from Nazi Germany during World War 2. this was taken action to re-establish their governments before 1939 and to secure Europe from Communism. This was known as The "Truman Doctrine"
But the Soviet Union ignored the Truman Doctrine and continued the occupations of Poland, Romania, Czechoslovakia, Hungary, Bulgaria, Yugoslavia, Eastern Germany. The Soviets put up Communist Governments to these countries to act as Soviet Satellite states and this is one of the causes of the Cold War.