Which theory suggested that if one country fell to communism, neighboring countries would follow?

• A. Truman Doctrine
• B. Domino Theory
• C. Containment
• D. Massive Retaliation

Answer: (B)

The key idea here is the Domino Theory—the belief that if one country falls to communism, its neighbors would be likely to follow in a chain reaction. Proponents argued that political instability, fear of encirclement, and the spread of communist influence could topple governments nearby, so the United States would need to intervene early to stop the spread.

This differs from the Truman Doctrine, which centers on providing support to countries resisting subjugation by communism, not a prediction about regional collapse. It also differs from Containment, a broader strategy aimed at preventing the worldwide spread of communism using a variety of tools, not a specific domino effect. Massive Retaliation, on the other hand, is about deterrence through the threat of major nuclear punishment, not about how regimes influence one another across borders.