Final answer:
The domino theory suggested that the fall of one country to communism would lead to the subsequent fall of neighboring countries, influencing U.S. involvement in conflicts such as Korea and Vietnam.
Step-by-step explanation:
The domino theory was an influential concept during the Cold War, which posited that if one nation in a region came under the influence of communism, then the surrounding countries would also fall to communism, much like a row of dominos toppling over. This theory was instrumental in shaping U.S. foreign policy and was cited by President Dwight Eisenhower when justifying American intervention in Southeast Asian countries like Vietnam and Laos. It was based on the fear that the spread of communism would continue unchecked unless actively opposed, leading to a potential global domination by America's adversaries.
During the Truman and Eisenhower administrations, the theory was seen as a justification for the U.S. to support non-communist regimes around the world, creating a global stance aimed at containing the spread of communism. This perspective led to U.S. involvement in conflicts such as Korea and Vietnam, where the U.S. acted to prevent communism from taking over, fearing that one country's fall to communism would trigger a chain reaction throughout the region.