The domino principle or domino theory was used by successive United States administrations during the Cold War to clarify the need for American intervention around the world. It stated that if one land in a region came under the influence of communism, then the surrounding countries would follow in a domino effect. President Eisenhower invoked the principle in a 1954 press conference:
“Finally, you have broader considerations that might follow what you would call the “falling domino” principle. You have a row of dominoes set up, you knock over the first one, and what will happen to the last one is the certainty that it will go over very quickly. So you could have a beginning of a disintegration that would have the most profound influences.”
— President Dwight D. Eisenhower The Domino Principle April 7, 1954