Joseph Stalin took myriad actions to spread Communism between 1945–1949. Spreading Communism throughout the world had always been a key goal of Moscow. World War II (1939–1945) was really only a truce in the hostility between Stalin and the West. It was not surprising, therefore, that Stalin aggressively tried to spread Communism after the war ended.
Stalin's determination to spread Communism was most evident in Eastern Europe. Poland, Czechoslovakia, Yugoslavia, Hungary, Romania, and Bulgaria had been overrun by Russian troops during the war, and Stalin established Communist governments in all of these countries. The Baltic states were also annexed into the USSR. East Germany, a Communist state, was founded in 1949. Greek Communists supported Stalin, but they lost a civil war in that country; Greece stayed on the side of the West.
In Western Europe, Stalin supported strong Communist parties in France and Italy.
In Asia, Stalin supported Communist forces in China, Korea, and Vietnam. China became Communist, as did North Korea.
One of the key events of the era was the Berlin Blockade. In 1948, Stalin tried to cut off West Berlin from West Germany; he wanted to add West Berlin to Communist East Germany. The West airlifted supplies to the city and kept Communist influence at bay in Germany.
Stalin's aggressive actions during this period helped cause the Cold War with the West.