Gulf of Tonkin Incident: In August 1964, the North Vietnamese torpedo boats allegedly attacked two American destroyers in the Gulf of Tonkin. In response, Congress passed the Gulf of Tonkin Resolution granting president lyndon B. Johnson broad authority to use military force in Vietnam. This marked a significant escalation in U.S. involvement and paved the way for more troops to be deployed.
Escalating U.S. Military Involvement: The United States had been providing military assistance to South Vietnam since the early 1950s, but its involvement intensified in the early 1960s as the conflict between North and South Vietnam grew more intense. By 1964, there were over 23,000 U.S. military advisors in Vietnam.
Dominos Theory and Containment: American policymakers were concerned about the spread of communism in Southeast Asia according to the "domino theory." They feared that if one country in the region fell to communism, others would follow, leading to a wider communist bloc. The United States wanted to prevent this by containing the spread of communism and supporting anti-communist governments.
Political and Public Opinion: There was a general belief in the U.S. government and public opinion that communism posed a threat to American national security and democratic values. There was also an ideological commitment to supporting South Vietnam as an ally in the global struggle against communism. The administration of President Johnson sought to demonstrate resolve in the face of aggression.
South Vietnamese Government Requests: The South Vietnamese government, led by President Ngo Dinh Diem, repeatedly requested military assistance from the Unite States to help combat the communist insurgency in the South. The U.S. responded with increased aid, military advisors, and eventually combat troops.
Fear of a Wider Conflict: Some American policymakers believed that if the United States did not intervene decisively in Vietnam, it would lead to a larger and more costly war later on or to a loss of prestige and credibility in the international arena.
These factors, among others, contributed to the escalation of U.S. involvement in Vietnam and ultimately led to the all out war that lasted until the early 1970s.