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

Why this is the answer

Communism, and more precisely the fear that it would spread. The Soviet Union was a powerful state built on communist principles, and the United States and its allies believed a democratic government and a capitalist economy were the better way to protect individual rights and freedoms. What they feared was expansion: communism taking hold in countries beyond the Soviet Union. The Cold War began shortly after the Second World War and ran for more than forty years, ending with the fall of the Berlin Wall in 1989, the reunification of Germany in 1990 and the breakup of the Soviet Union in 1991. Memory hook: one word answers it, and the word is communism.