The origins of the Cold War between the US and the Soviet Union arose during World War II. The Soviet Union wanted the Allies to open a second front against the Nazis, but the US and the other Allies delayed their attack on mainland Europe until D-Day in June of 1944. The Allies' delay in opening a European front angered the Soviets. In addition, while the Soviet Union moved eastward towards Berlin at the end of the war, they took over parts of Eastern Europe, including Poland.

After the war, the US and its allies, including England, disliked what they termed the "Iron Curtain" that had descended around the Soviet Union and its satellite states. The Soviets also distrusted the Americans after the detonation of atomic bombs over the Japanese cities of Hiroshima and Nagasaki and began developing their own atomic weapons, triggering an arms race between the two nations.

American foreign policy during the 1950s centered on trying to prevent the spread of Communism—a policy called "containment." This caused the US to get involved in proxy wars, such as the wars in Korea and Vietnam, in an attempt to prevent those nations from being taken over by Communists. In addition, the culture of the 1950s was marked by fear, including McCarthyism, which was a war on alleged domestic Communists. Americans feared a Communist takeover of their country.