The Cold War was a direct result of aggressive Soviet policies for expansion during the immediate post-war years. Stalin's government violated solemn promises  made in the Yalta Accords, imposed Soviet dominated governments on the unwilling nations of Eastern Europe, and schemed to spread communism throughout the world. American policy, a logical and necessary response, made a firm commitment to oppose Soviet expansion and retain its armed forces in a continual state of preparedness.

Throughout the twentieth century, the United States' role  in world affairs was influenced by one overriding goal: to maintain an "open door" for American trade in world markets. The Cold War, therefore, was less a response to Russian aggression than an expression of the American belief in the principles of capitalism and the desire to keep the doors of trade open with Eastern Europe and Asia.

The use of atomic bombs on Hiroshima and Nagasaki caused the Cold War. American decision makers used the bombs on an already defeated Japan, not to win the war, but to impress and intimidate the Soviets. However, atomic diplomacy had just the opposite effect: it convinced the Soviets that Americans had negative intentions towards them.