Before the United States decided to increase its involvement in the Vietnam War, France waged a seven year war (1946 to 1954) against Ho Chi Minh and his Vietnamese resistance movement. This conflict (sometimes called the First Indochina War) came about because the Vietnamese had tired of French rule, but the French refused to give up their colonies in Indochina. Although the United States remained neutral at first, the Cold War soon began to intensify and U.S. politicians became more and more anxious to halt the spread of communism. At first, President Truman authorized covert support for the French, but by 1950 the U.S. was openly providing financial support for the French war effort. By 1954, the French had been badly defeated and Vietnam was divided into North and South, with the northern half going to Ho Chi Minh who was not satisfied with this partial victory and remained determined to unite North and South Vietnam under communist rule. From that point forward, U.S. involvement would continue to grow until hostilities eventually resumed.

On September 26, 1945, Lt. Col. A. Peter Dewey became the first American soldier to die in Vietnam. Apparently mistaken for a Frenchman, Dewey was gunned down by Vietminh troops while driving a jeep to the airport. The son of a former Illinois congressman, he had been the head of the American O.S.S. mission. However, because the conflict had not yet fully developed at this time, some sources consider the first U.S. casualties of the Vietnam War to be Major Dale R. Buis and Master Sergeant Chester M. Ovnand who were killed in 1959 during a guerilla attack at Bienhoa.

On August 2, 1964, three North Vietnamese gunboats allegedly fired torpedoes at the U.S.S. Maddox, a destroyer which was positioned in international waters near the Gulf of Tonkin (approximately thirty miles off the coast of North Vietnam). This attack, which was disputed by the North Vietnamese, became known as the Gulf of Tonkin Incident. It resulted in the swift passage by the U.S. Congress of the "Gulf of Tonkin Resolution" which gave President Lyndon Johnson authorization to "take all necessary measures to repel any armed attack against forces of the United States and to prevent further aggression." This legislation effectively gave Johnson the power to wage all out war against North Vietnam without seeking any further approval from Congress. The Pentagon Papers, leaked in 1971 by Department of Defense worker Daniel Ellsberg, have since revealed that the Johnson administration essentially fabricated these attacks in order to gain support for the war.

In 1965, the United States launched Operation Rolling Thunder, a sustained bombing campaign designed to stop the flow of men and supplies down the Ho Chi Minh Trail and break the will of the North Vietnamese. Originally scheduled to last only eight weeks, these nearly continuous air raids would continue for more than three years. But the bombings were largely ineffective and did little to stop the flow of weapons and fighters into North Vietnam. It has been estimated that, during Operation Rolling Thunder, the U.S. dropped almost a million tons of bombs on North Vietnam -- more bombs than it had dropped in all of World War II.

The U.S. Military used many herbicides/defoliants during the Vietnam War, including Agent Blue, Agent Green, Agent White, Agent Purple, Agent Pink, and Agent Orange. Agent Orange, however, has become the most infamous of this group because it was later shown to have toxic dioxin contaminants which have been blamed for various health problems and birth defects among both the general Vietnamese population and U.S. soldiers who were exposed to recently sprayed areas. The stated purpose of Agent Orange was to defoliate or remove the leaves from trees in heavily wooded areas in order to limit cover for guerrilla fighters who might be hiding there. Due to the controversy surrounding it, however, the use of Agent Orange by the U.S. military was discontinued in 1971. 2,4,5-T (2,4,5-trichlorophenoxyacetic), a component of Agent Orange, has since been banned in the U.S. and many other countries.

On January 30, 1968, the North Vietnamese launched simultaneous attacks on almost every major city in South Vietnam. These attacks, which came to be known as the Tet Offensive, were planned to coincide with Tet Nguyen Dan, the lunar new year festival, one of the most important Vietnamese holidays. North Vietnamese forces briefly took control of several important cities during the Tet Offensive. In fact, the worst single massacre of the Vietnam War took place during the temporary Communist occupation of Hue, when 3,000 civilians were brutally murdered and buried in a mass grave. South Vietnamese and U.S. forces were quick to characterize the Tet Offensive as a failure since all North Vietnamese gains made during the attack were eventually reversed, but it was a major psychological victory for the North which had previously been characterized as being on the verge of collapse. The American people, many of which were beginning to question the wisdom of this war, could no longer be convinced that there was a light swiftly approaching at the end of the tunnel.

Ngo Dinh Diem, the first President of the Republic of Vietnam, was assassinated on November 2, 1963, in a coup led by his own generals. Diem had grown increasingly unpopular largely because of his imprisonment and execution of hundreds of Buddhists, and the United States, which previously backed Diem's regime, had apparently grown weary of their association with such an unpopular leader as they made no attempts to discourage the assassins and, according to some reports, perhaps even encouraged them. Soon after Diem's death, general Nguyen Khanh seized power in Saigon in a bloodless coup. Major General Duong Van Minh, who was believed to have planned Diem's assassination, was placed under house arrest, but remained in the circle of power as chief-of-staff. In 1975, he would briefly serve as President of South Vietnam before the fall of Saigon.

On March 16, 1968, U.S. soldiers from the 11th Brigade, Americal Division of Charlie Company took part in the "My Lai Massacre" when they entered the village of My Lai, an area which had long been suspected of being a haven for the Viet Cong, and began indiscriminently killing unarmed Vietnamese civilians. According to some reports, they assembled over 500 villagers, mostly women, children, and the elderly, and then shot them. Through the efforts of journalist Seymour Hersh, the atrocities committed at My Lai eventually came to light and lit a political firestorm under an already divided American public. In 1971, Lt. William Calley, who reportedly gave the order to shoot everyone in the village, was convicted of murder for his part in the My Lai Massacre and sentenced to life in prison. U.S. President Richard Nixon, however, ordered him released from prison only one day after his sentencing. In the end, Calley's lifetime sentence was reduced to just 3 1/2 years of house arrest at his quarters in Fort Benning, Georgia. Calley always claimed that he was following the orders of his immediate superior, Captain Ernest Medina. In a separate trial, Medina was found innocent of all charges related to the massacre.

58,226 Americans were killed or listed as "Missing in Action" during the Vietnam War. Another 153,303 Americans were wounded, bringing the total number of U.S. casualties to 211,529.

It is extremely difficult to estimate the number of Vietnamese killed during the Vietnam War. For years, the North Vietnamese, for political reasons, refused to release these numbers. They did not, perhaps, want the immense human cost of the war to tarnish their victory. In 1995, years after the fact, they finally released a report putting the number of Vietnamese combatants killed at 1.1 million and the number of Vietnamese civilians killed at almost 2 million. If these numbers are accurate, that would put the total number of Vietnamese killed or missing during the Vietnam War at approximately 3 million. Another 600,000 combatants were listed as wounded. There are no figures on the number of wounded civilians.