Final answer:
The domino theory was the belief that if one country fell to communism, others in the region would follow, like a chain of falling dominos. This view shaped U.S. foreign policy during the Cold War and led to America's military and economic interference to prevent the spread of communism, particularly in Southeast Asia.
Step-by-step explanation:
The domino theory was a belief that if one country fell to communism, others would fall as well. This theory influenced US foreign policy during the Cold War, particularly in Southeast Asia, as American policymakers believed that the spread of communism from one nation to its neighbors was akin to a chain of dominos toppling one another. President Eisenhower's administration applied the domino theory in advocating for the containment of communism, which was seen as a threat to democratic nations and global stability. The increasing influence of communism in China and Vietnam triggered U.S. intervention based on the assumption that a 'fall' to communism would lead to regional, and potentially global, domination by communist powers.
Originally articulated as part of the policy of containment, the domino theory was used to justify American involvement in various nations to prevent the proliferation of communism. This strategy continued to influence American foreign policy in regions deemed susceptible to communist influence and was cited as a rationale for supporting regimes that opposed communism, regardless of their democratic credentials.