The term "Domino Theory" relates to the political belief during the Cold War that if one country in a region fell to communism, neighboring countries would follow in a cascading effect, much like a row of falling dominoes. This idea was particularly influential in U.S. foreign policy in Southeast Asia. It justified American involvement in conflicts such as the Korean and Vietnam Wars, where the U.S. aimed to prevent the spread of communism. The Domino Theory reflected a fear of communism's expansion and shaped military and political strategies throughout the Cold War era.