Answer :
The correct answer is:
The Domino Theory
1. The Domino Theory was a belief during the Cold War era that if one country in a region came under the influence of communism, then neighboring countries would follow in a domino effect.
2. This theory was used to justify the United States' involvement in conflicts such as the Vietnam War, where the fear was that if Vietnam fell to communism, then other countries in Southeast Asia would also fall.
3. The Domino Theory influenced US foreign policy decisions as they aimed to prevent the spread of communism and contain its influence to specific regions.
Therefore, the Domino Theory is the idea that if one nation falls to Communist control, nearby nations will follow in a domino effect.
