1. Domino Theory: The belief that if one Southeast Asian country fell to communism, others would follow in a chain reaction, leading to a significant expansion of communist influence in the region.
2. Containment Policy: The Cold War policy aimed at preventing the spread of communism. Vietnam was seen as a key battleground in this broader global struggle between the United States and the Soviet Union.
3. Gulf of Tonkin Incident: In 1964, the U.S. destroyer USS Maddox was allegedly attacked by North Vietnamese torpedo boats in the Gulf of Tonkin. This incident led to the passing of the Gulf of Tonkin Resolution, which gave President Lyndon B. Johnson broad authority to wage war in Vietnam.
4. Defense of South Vietnam: The U.S. committed to supporting the anti-communist government of South Vietnam and preventing its takeover by North Vietnam, which the U.S. viewed as a threat to regional stability.
5. Reputation and Credibility: The U.S. feared that backing down from its commitment to South Vietnam would damage its reputation and credibility as a global superpower and undermine its ability to influence events in other parts of the world.