The Vietnam War was a long-standing conflict (1954 through 1975) between North Vietnamese communists seeking to unify the country and a fledgling, oppositional government in South Vietnam backed by the United States. Upon realizing the South Vietnamese army couldn’t fend off communist invasion, President Lyndon B. Johnson contemplated whether to pull out or launch a massive assault. To demonstrate his unwavering stance on communist containment, President Johnson authorized large-scale U.S. military intervention in 1964 that swelled to 575,000 troops within five years.

Fear of Communism and Nuclear War

Military escalation in Vietnam was tied to a growing fear of communists in the Soviet Union and China annihilating the free world. Ideologically, communism was considered the antithesis of democracy and freedom. Fears were heightened when the Soviet Union started testing nuclear bombs. In his September 29, 1967, speech to the American public, President Johnson warned that communist takeover of Southeast Asia increased the risk of a third world war with deployment of nuclear weapons. Other democratic countries looked to the United States to lead the global anti-communism fight.

The Domino Theory

Presidents John F. Kennedy and Lyndon B. Johnson used the domino theory to justify costly military aid to non-communist South Vietnam. The domino theory, a foreign policy concept introduced in 1954 by President Dwight D. Eisenhower, held that if one country falls to communism, neighboring countries would tumble in quick succession. Despite a growing anti-war movement, President Johnson maintained that a strong show of American force was needed in Vietnam to prevent communism from spreading throughout Southeast Asia.

Struggling South Vietnamese Army

Massive United States intervention protected the passive South Vietnamese army from imminent defeat by the Northern Vietnamese army and the communist National Liberation Front. Initially, United States involvement was limited to sending economic aid and 16,300 military advisers to Vietnam, but this proved ineffective. U.S. concerns mounted when South Vietnam lost control of the fertile Mekong Delta in 1963. South Vietnamese soldiers weren’t as loyal to the cause as members of the National Liberation Front. For instance, 90,000 South Vietnamese soldiers deserted the army, compared to fewer than 20,000 NLF fighters, according to History.com.

Tonkin Gulf Crisis

A flashpoint in the intensifying conflict occurred in 1964 when destroyer ship USS Maddox was torpedoed in the Gulf of Tonkin by the North Vietnamese navy using Soviet-built torpedo boats to launch the attack. President Johnson ordered retaliatory strikes; about 30 enemy ships were destroyed. Congress then passed the Tonkin Gulf Resolution empowering the president to take whatever action he deemed appropriate to fight the communists, which further emboldened the president to ramp up the U.S. military offensive.