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The Vietnam War (1945–1975)

History SparkNotes

Quagmire and the Tet Offensive: 1966–1968

Johnson and Escalation: 1964–1966

The U.S. Antiwar Movement: 1960–1970

January 1967 United States reaches nearly 400,000 troops in Vietnam
June 1967 CIA initiates Phoenix Program
January 1968 NVA attacks U.S. Marine base at Khe Sanh North Vietnamese launch Tet Offensive
February 1968 McNamara resigns as secretary of defense
March 1968 Westmoreland causes uproar by requesting 200,000 more troops U.S. soldiers kill 500 Vietnamese civilians in My Lai Massacre
Key People
Lyndon B. Johnson -  36th U.S. president; insistence that the United States was winning the war in Vietnam led to the development of the “credibility gap”
Robert McNamara -  Johnson’s secretary of defense; had initially supported escalation but began to question U.S. involvement and resigned in early 1968
William C. Westmoreland -  Commander of U.S. military in Vietnam; made enormous political blunder by requesting Congress for 200,000 more troops after Tet Offensive of 1968
William Calley -  U.S. Army lieutenant in charge of company that killed 500 Vietnamese civilians at My Lai; was court-martialed in 1971 but paroled in 1974

Changing Strategies

By 1966, both sides in the Vietnam War started changing their strategies. General Nguyen Chi Thanh, a top Viet Cong commander, began to push for a general offensive. Meanwhile, General William C. Westmoreland’s search-and-destroy operations were fully under way. Although many of Westmoreland’s campaigns were successful in killing Viet Cong forces, they also required large numbers of U.S. troops.

By the end of 1966, nearly 400,000 U.S. soldiers were in Vietnam; this number would reach 500,000 by the end of 1968. President Johnson also authorized the use of chemical weapons such as napalm, a thick gasoline-based gel that can be sprayed and burns at high temperatures, and Agent Orange, a chemical defoliant that was used to destroy jungle vegetation to expose Viet Cong hideouts. Although both of these weapons were effective, they inflicted horrific devastation, and Agent Orange in particular caused unforeseen health problems among both troops and Vietnamese civilians, the effects of which have persisted for decades.


In late 1966, U.S. forces began to search for the so-called Central Office of South Vietnam, or COSVN—the Viet Cong command center that U.S. officials insisted existed somewhere in the jungle, directing Viet Cong operations throughout Vietnam. The existence of the COSVN has never been confirmed, however, and it is likely there never really was such a command center at all. Nonetheless, General Westmoreland initiated a series of search campaigns in the so-called Iron Triangle, a sixty-square-mile area north of Saigon. Although several thousand Viet Cong were killed in a campaign that lasted until 1967, U.S. forces failed to locate COSVN or make any progress in encircling or rooting out the Viet Cong.

The “Credibility Gap”

Despite the numerous setbacks, Johnson and other U.S. officials, citing increased troop numbers and redefined objectives, again claimed to be making headway in the war. Photos and video footage of dead American soldiers in newspapers and on evening news programs, however, indicated otherwise. Moreover, U.S. spending in support of the war had reached record levels, costing the government an estimated $3 billion a month. As a result, many people in the United States began to speak of a “credibility gap” between what Johnson and the U.S. government were telling the American people and what actually was transpiring on the ground.

Khe Sanh

Throughout 1967, Viet Cong guerrillas stepped up their attacks on U.S. servicemen. Then, in late January 1968, the North Vietnamese Army launched a major offensive against the U.S. Marine base at Khe Sanh, just below the DMZ. U.S. commanders, determined to hold the base, sent 50,000 men as reinforcements. Though one of the largest battles of the war, Khe Sanh was essentially a diversion planned by the Viet Cong in an effort to weaken American forces farther south, paving the way for a more significant offensive.

The Tet Offensive

Indeed, with U.S. forces still north at Khe Sanh, the Viet Cong launched the Tet Offensive, the large “general offensive” that Ho Chi Minh and the Vietnamese Communists had been planning for years. On January 30, 1968, on the Vietnamese new year holiday of Tet, separate Viet Cong and NVA cells attacked twenty-seven different U.S. military installations throughout South Vietnam at the same time.

Fighting was intense, but U.S. forces managed to kill or capture the bulk of the Viet Cong raiders within several weeks. The toughest combat occurred in the city of Hue, which the NVA actually conquered for a few weeks before U.S. troops took it back. Fighting occurred as far south as Saigon, taking over the streets. Amid the chaos, an Associated Press photographer captured South Vietnam’s chief of police, Nguyen Ngoc Loan, executing a Viet Cong captain in the streets of Saigon—a brutal image that shocked the American public and became a symbol of the Vietnam quagmire.

Effects of the Tet Offensive

Although the Tet Offensive was quashed relatively quickly, it was an enormous political defeat for the U.S. Army and for Johnson because it proved, despite Johnson’s pronouncements, that the war was far from over. The attack not only turned millions of Americans against the war but also split the Democratic Party and the entire U.S. government into antiwar and pro-war factions. In February 1968, Johnson’s own secretary of defense, Robert McNamara, resigned.

In March, when General Westmoreland and the leaders of the Joint Chiefs of Staff requested 200,000 more soldiers be sent to Vietnam, the American public and policy makers alike were dumbfounded. Westmoreland’s request in turn prompted many foreign policy officials, including former secretary of state Dean Acheson, to denounce the army’s strategy of victory by attrition. Johnson ultimately denied Westmoreland the additional troops.

One of the great ironies of the war was the fact that the Tet Offensive was actually a resounding tactical victory for the United States. The NVA gained no territory for more than a brief period, while 40,000 Vietnamese Communist troops died compared to about 3,000 Americans and South Vietnamese combined. The Tet Offensive thus severely damaged Ho Chi Minh’s armies. Nonetheless, the cost in terms of U.S. public opinion would far outweigh the military victory.

Worsening Public Opinion

In February 1968, American journalist Walter Cronkite famously commented on the CBS Evening News that the United States was mired in a stalemate and that the war probably could not be won. Indeed, the American public, which had long been reassured that the U.S. military was making progress, felt betrayed after the Tet Offensive. Over 500,000 U.S. troops were stationed in Vietnam, and nearly 30,000 had been killed, all in the name of a vaguely defined war that seemed suddenly unwinnable. No longer willing or able to straddle the widening credibility gap, Johnson announced at the end of March that he would not run for reelection in the 1968 election.

Waning Morale

The Tet Offensive also took a significant toll on morale among U.S. troops. With the apparent military victory of the offensive undermined by eroding support at home and a seeming lack of military goals or ideas, American soldiers became increasingly upset and disillusioned by the war. Drug abuse among American soldiers was growing rampant, and even cases of “fragging, in which soldiers killed their own superior officers in order to avoid being sent on missions, began to appear.

The My Lai Massacre

This discontentment among U.S. troops resulted in one of the most horrible incidents of the war, in March 1968. Soldiers in one U.S. company, frustrated at their inability to find Viet Cong during a search-and-destroy mission in the tiny South Vietnamese village of My Lai, killed approximately 500 unarmed Vietnamese civilians, including women, children, and elderly. The My Lai Massacre was covered up and did not become public knowledge until late 1969. In 1971, Lieutenant William Calley, commander of the company, was sentenced to life imprisonment for war crimes. Despite shock at the massacre, however, many in the American felt that Calley was a scapegoat for wider problems, and he was released on parole in 1974.

The Phoenix Program

After the Tet Offensive, the U.S. government stepped up its covert operations, the most famous of which was the CIA-led Phoenix Program, which had been initiated in June 1967. Among other objectives, the program was meant to assassinate Viet Cong leadership. Although approximately 20,000 people were assassinated under the Phoenix Program, the program was plagued by corruption, mismanagement, and faulty intelligence, and many of its victims were likely not Viet Cong at all. In many cases, unscrupulous South Vietnamese officials named their opponents as Viet Cong and requested that the Phoenix Program eliminate them. When the details of the program later surfaced, many protested that its activities amounted to nothing more than war crimes.

The U.S. Election of 1968

Johnson’s early withdrawal from the 1968 U.S. presidential race allowed other Democrats to step in, including two antiwar candidates from the Senate, Eugene McCarthy and Robert F. Kennedy, and Johnson’s pro-war vice president, Hubert Humphrey. Kennedy, the younger brother of former president John F. Kennedy, seemed sure to win the party’s nomination until he was assassinated at a Los Angeles hotel in June 1968. Humphrey became the Democratic nominee instead. However, violence outside the Democratic National Convention in Chicago (see The Chicago Riot and Kent State, p. 50 ) ruined Humphrey’s chances, as American voters erroneously linked the police brutality with the Democratic Party.

Republicans capitalized on the riot and nominated Eisenhower’s former vice president, Richard M. Nixon, on a pro-war platform. Alabama governor George C. Wallace also ran as a third-party candidate, for the war and against civil rights. Because the riot had tainted Humphrey’s public image and because Wallace seemed far too conservative, Nixon won the election easily.

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