6. Harry S. Truman
In spite of these early successes, Truman’s diplomatic situation was beset with challenges. Although the Soviet Union had been a powerful ally to the United States during the war, international relations deteriorated quickly when it became apparent that the Soviets intended to remain in control of Eastern European nations that were expected to be reestablished according to their pre-Hitler governments. This, along with the exclusion of the Soviets from the reconstruction of Asia, began the Cold War.