The domino theory was a theory prominent from the 1950s to the 1980s, that speculated that if one country in a region came under the influence of communism, then the surrounding countries would follow in a domino effect.
The domino theory was used by successive United States administrations during the Cold War to justify the need for American intervention around the world.
Though he never directly used the term “domino theory”, U.S. President Dwight D. Eisenhower put the theory into words during an 7 April 1954 news conference, when referring to communism in Indochina:
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.