Why was Vietnam America's longest war? How did each of the presidents who served during the period in question view the situation in Southeast and what policies did they pursue regarding the conflict?
Truman: Truman presided over the close of the Second World War, especially with regard to the fighting in the Pacific. Japan had occupied much of Southeast Asia, including Vietnam. The Vietnamese guerrillas who led the fight against the Japanese, led by Ho Chi Minh, now sought independence from all occupiers. Following its liberation from German occupation, France sought to reoccupy its former colonies in Southeast Asia. Truman had an opportunity to cooperate with Ho, or stay completely out of the looming war between France and the Vietnamese, but agreed to support French policies in exchange for French cooperation in Western Europe. As George Herring points out in his history of the Vietnam War, Truman and his advisors also saw the communist movement led by Ho as representing a potential menace to the spread of democracy he envisoned.
Eisenhower: The effort to contain communist expansionism in Southeast Asia became a growing priority in Washington, D.C. Eisenhower referred to the threat of the growing strength of the Viet Minh, the communist guerrilla army fighting the French and named for Ho, as a threat to all of Southeast Asia. Employing the analogy of falling dominoes, he postulated that if Vietnam fell to the communists, it would lead to the fall of all the region's countries to communism, like dominoes falling one after another. Eisenhower sought to build up South Vietnam as an independent and democratic nation, while political pressure in Congress grew to intervene more forcefully in Vietnam.
Kennedy: As a senator, Kennedy had been a proponent of militarily involvement in Southeast Asia to contain communism. As president, he began to accelerate U.S. involvement there, dispatching military advisors to help the South Vietnamese defend themselves against the better armed and far more disciplined North Vietnames, still lead by Ho and his top general Vo Nguyen Giap. A serious admirer of special operations forces, he advocated the establishment of expanded and more formalized U.S. special forces units, mainly the "Green Berets" (Army Special Forces) and the Navy's Sea, Air, Land (SEAL) commandos. These special units became Kennedy's main instrument for influencing events in Southeast Asia.
Johnson: LBJ entered office with ambitions for a New Society, including progress on civil rights, welfare programs for the poor, and more. His Great Society languished instead while his presidency became subsumed by the growing war in Vietnam. LBJ continuously authorized large increases in the number of American troops U.S. military leaders argued were essential to contain North Vietnam's efforts at vanquishing the south. Under his watch, U.S. involvement in Vietnam grew from advisory to a full-scale war. The main event was the Tonkin Gulf incident, which he exploited to convince Congress to authorize the bombing of the north.
Nixon: Together with Henry Kissinger, conducted a two-track policy of air strikes on North Vietnam while negotiating a peace agreement with its leaders. Nixon's policies were strenuously opposed by many liberals, and rioting on university campuses resulted. His main policy initiative was known as "Vietnamization," meaning U.S. troops would withdraw and the South Vietnamese Army, supported with U.S. military aid, would continue to fight. A congressionally-imposed limit on the amount of aid is argued to have caused the collapse of the South Vietnamese military effort, with the consequent victory of the North.