The Cold War was caused by mistrust, differing political systems and the disagreement over the rebuilding of Berlin and Europe. The question of war reparations caused a divide between the Soviet Union and the Allies.
While the Cold War can be attributed to certain causes, the tensions between leaders before 1945 had a part to play in increasing the suspicions of the USSR and the West. Josef Stalin, as head of the USSR, refused to join the United Nations for several years. He was also upset about the delaying of D-Day as he believed it was a plot to allow the Soviet Union more casualties. During the 1943 Tehran Conference, Stalin and British Prime Minister Winston Churchill clashed regarding the control Stalin had on eastern European countries.
Germany became a point of contention after the war, with Berlin divided between the East and the West. By 1948, Germany's economy was failing and the West proposed a combined zone and expanded currency reform. The Soviets responded by blocking access and eventually constructed the Berlin Wall.
Stalin's reasoning for his actions were the reparations of war. The Soviet Union had lost over more than 20 million lives during the war and was adamant for security and reparations; the Allies insisted on restraining the Soviet domination of Eastern Europe and the spread of Communism. These factors propagated the Cold War.