What were among the main U. S. foreign policy concerns following the Second World War and why?

Because Nazism persisted on a large scale following the war, the United States and the Soviet Union maintained their strong alliance and shared intelligence with one another; the onset of the Cold War several decades later, therefore, came as a shock to American leaders.

Having become accustomed to the idea of fighting modern world wars, national leaders across the globe were less cautious than ever before and proved eager to employ new technologies such as atomic bombs as a means of advancing their own ends.

With the elimination of German Nazism, the United States and the Soviet Union no longer seemed to share a united goal; the power vacuums in Europe and Asia due to the defeat of the Germans and Japanese left the Americans and Soviets competing for global influence.

Because the Second World War had exhausted so many American resources, domestic concerns significantly overshadowed foreign affairs during the postwar years; any foreign policy concerns, therefore, centered predominantly on European trade laws.