Credibility, the domino theory and fear of a communist victory led the USA from advisers to a large ground war.
Eisenhower sent aid and advisers. Kennedy increased the number of US military advisers to about 16,000 by 1963. American leaders believed in the domino theory: if South Vietnam fell, communism would spread across Southeast Asia.
In August 1964, after reported clashes with North Vietnamese boats, Congress passed the Gulf of Tonkin Resolution. It gave President Johnson broad authority to use force in Southeast Asia without a declaration of war.
In March 1965, Johnson began Operation Rolling Thunder, a sustained bombing campaign against North Vietnam, and sent the first combat troops. By 1968 more than half a million American troops were in Vietnam.
Johnson's reasons combined credibility, containment and domestic politics. In April 1965 he said the USA had a promise to keep and that abandoning South Vietnam would shake allies' confidence in American commitments. He also feared the political cost of being blamed for "losing" Vietnam, as Truman had been blamed for China.
- Advisers
- About 16,000 by 1963.
- Gulf of Tonkin Resolution
- August 1964.
- Rolling Thunder
- Bombing of the North from March 1965.
- Peak deployment
- More than half a million US troops by 1968.
Worked example: Linking credibility to escalation
Why did Johnson escalate in 1965?
- Weakness: the Saigon government seemed close to collapse after 1963.
- Credibility: Johnson argued allies from Berlin to Thailand relied on US promises.
- Containment: the domino theory linked Vietnam to all Southeast Asia.
- Limits: he kept the war limited to avoid war with China or the USSR.
Watch out for this
The USA declared war on North Vietnam in 1964.
Congress never declared war. The Gulf of Tonkin Resolution gave Johnson authority to use force.
Check your understanding
What did the Gulf of Tonkin Resolution do?
- It gave the president broad authority to use force in Southeast Asia.
- It declared war on China.
- It ordered US troops home.