The use of Domino Theory in the Vietnam War showed which fear?

Correct answer: Fear that spread of communism in one country could affect neighboring countries

The direct answer is A: the fear that communism spreading in one country could affect neighbouring countries. Domino Theory compared countries to standing dominoes: if one fell, nearby ones might fall next. During the Cold War, American policymakers feared that a communist victory in Vietnam would encourage or help communist movements in other Southeast Asian countries. This belief supported containment, the policy of trying to limit the spread of communism. Option A is correct because it expresses the central idea of the theory. Option B is wrong because the theory concerned communist expansion, not fear of democracy spreading. Option C is wrong because stopping sea trade was not the theory’s main meaning. Option D is wrong because ending monarchies was not its specific concern. The theory was a political assumption and was debated; it should not be treated as an automatic law. Memory cue: one communist state falls into the communist camp, then neighbours may follow like dominoes.