domino theory

a theory that if one country is taken over by an expansionist, esp. Communist, neighbor, party, or the like, the nearby nations will be taken over one after another.

[1960-65]

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or domino effect

Doctrine of U.S. foreign policy during the Cold War, according to which the fall of a noncommunist state to communism would precipitate the fall of other neighbouring noncommunist states.

The theory was first enunciated by Pres. Harry Truman, who used it to justify sending U.S. military aid to Greece and Turkey in the late 1940s. Dwight D. Eisenhower, John F. Kennedy, and Lyndon B. Johnson invoked it to justify U.S. military involvement in Southeast Asia, especially the prosecution of the Vietnam War.

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▪ international relations

also called  Domino Effect,  

      theory in U.S. foreign policy after World War II stating that the “fall” of a noncommunist state to communism would precipitate the fall of noncommunist governments in neighbouring states. The theory was first proposed by President Harry S. Truman (Truman, Harry S.) to justify sending military aid to Greece and Turkey in the 1940s, but it became popular in the 1950s when President Dwight D. Eisenhower (Eisenhower, Dwight D.) applied it to Southeast Asia, especially South Vietnam. The domino theory was one of the main arguments used in the Kennedy and Johnson administrations during the 1960s to justify increasing American military involvement in the Vietnam War.

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