Which of the following was a significant concern in post-World War II America?

The significant concern in post-World War II America was communism. Following the end of the war, the U.S. emerged as a global superpower and faced the challenge of containing the spread of communism, particularly from the Soviet Union. This fear was rooted in the ideological struggle between communism and capitalism, leading to policies such as the Truman Doctrine and the establishment of NATO aimed at preventing the influence of communist ideology in Europe and around the world. The Red Scare, which swept across the country in the late 1940s and 1950s, was fueled by paranoia about communist infiltration in government and society, significantly impacting domestic and foreign policy decisions.

Expansionism, neutrality, and colonialism were indeed relevant concepts in different contexts, but during this specific period, the threat of communism dominated public and political discourse, driving significant actions, including military involvement in conflicts like the Korean War.