Which theory described the fear that if one country fell to communism, neighbors would follow?

• A. The Containment Theory
• B. The Domino Theory
• C. The Truman Doctrine
• D. The Marshall Plan

Answer: (B)

The idea being tested is the domino effect—the fear that if one country falls to communism, its neighbors would follow one after another. This line of thinking framed much of early Cold War policy, because leaders worried a single regional victory could trigger a rapid spread of communist influence across nearby nations, expanding the Soviet sphere. The domino theory helps explain why the United States pursued actions designed to prevent any country from tipping, especially in Asia and other regions.

Containment refers to preventing the spread of communism in general, not the specific chain-reaction worry. The Truman Doctrine focused on providing support to countries resisting subjugation by communist forces, as a policy stance, rather than describing a regional domino effect. The Marshall Plan aimed to rebuild Western Europe economically to reduce conditions that could foster communist appeal, not to describe a cascading fall of neighboring states.