Why did the Cold War start?

The cold war, an ideological conflict between Communist and non-Communist countries, started after World War II (1939-45) when the Allies (United States, Britain, France, and the Soviet Union) disagreed over how to govern occupied Germany. Although the Soviet Union and the Western Allies were supposed to rule Germany jointly, the arrangement was beset by the spread of communism. During the war Soviet leaders had joined the United States and Western European countries to fight the Germans, but the Soviets supported communism, a political and economic system that they believed had to combat and overtake capitalism, which was practiced elsewhere in the Western world. By 1947 the United States had formulated policy to prevent the Soviet Union from exporting communism to other countries.