During the Cold War, what was the main concern of the United States?

The primary concern of the United States during the Cold War was the threat posed by communist expansion. After World War II, the ideological battle between capitalism, represented by the United States, and communism, led by the Soviet Union, defined international relations. The U.S. was focused on containing the spread of communism, believing that if one country fell under communist influence, neighboring countries might follow—a theory known as the "domino theory." This concern prompted the U.S. to engage in various activities, including military interventions, forming alliances such as NATO, and participating in conflicts like the Korean and Vietnam Wars, all aimed at curbing the influence of communist ideologies worldwide.

The other options do not align with the central focus of U.S. policy during this era. While terrorism and environmental issues have become significant concerns in more recent decades, they were not primary factors in Cold War strategies. Similarly, colonial rule was an important global issue but not the central concern of U.S. foreign policy, which was predominantly framed by the conflict with communism.