The domino theory/effect in the context of the Cold War was a belief that if one country in a region fell to communism, then neighboring countries would also fall like a row of dominoes. This theory influenced U.S. foreign policy during the Cold War, leading to interventions in countries like Vietnam to prevent the spread of communism. The fear of communism spreading and the need to contain its influence shaped many decisions made by the U.S. during this period.
