The domino theory significantly influenced the United States' role in the Vietnam War by convincing the United States to become involved in the war. The theory posited that the spread of communism in one country could lead to the spread of communism in neighboring countries, much like a falling domino. U.S. policymakers feared that if Vietnam fell to communism, neighboring countries in Southeast Asia, such as Laos, Cambodia, and Thailand, would also fall, threatening U.S. interests and the stability of the region.
This belief was a major factor in the U.S. decision to escalate its military involvement in Vietnam during the 1960s, as the government aimed to prevent the further spread of communism and to support the South Vietnamese government against the communist North. The domino theory underscored the urgency of U.S. intervention, leading to a commitment of troops and resources to the conflict, despite growing dissent and controversy surrounding the war over time.