The Vietnam War (1955-1975) was a prolonged armed conflict in Southeast Asia fought between the communist Democratic Republic of Vietnam (North Vietnam), supported by the Soviet Union and the People's Republic of China, and the Republic of Vietnam (South Vietnam), supported by the United States and other anti-communist allies. The war grew out of the First Indochina War (1946-1954) against French colonial rule and became a central theater of the broader Cold War struggle between the United States and the Soviet Union. American military involvement escalated sharply after the Gulf of Tonkin Resolution of 1964 and peaked in the late 1960s before a gradual withdrawal under the policy of Vietnamization. The conflict ended on 30 April 1975 with the fall of Saigon and the reunification of Vietnam under communist rule the following year.

Vietnam had been under French colonial administration as part of French Indochina since the late nineteenth century. Following World War II, Ho Chi Minh's Viet Minh movement - combining Vietnamese nationalism with Marxist-Leninist ideology - declared independence and fought the First Indochina War against France. The 1954 Geneva Accords, following France's defeat at Dien Bien Phu, temporarily divided Vietnam at the 17th parallel pending nationwide elections that were never held. The United States, fearing a communist electoral victory under the domino theory framework, backed the government of Ngo Dinh Diem in the South. Armed insurgency by the National Liberation Front (NLF), commonly called the Viet Cong, began in the late 1950s with North Vietnamese support.

American military advisors were present in South Vietnam from the late 1950s under the Eisenhower administration. President Kennedy expanded this presence before his assassination in 1963. Following the Gulf of Tonkin incident in August 1964 - the circumstances of which remain disputed - Congress authorized President Johnson to expand U.S. military operations without a formal declaration of war. Ground troop deployments began in 1965 and reached a peak of approximately 543,000 in 1969. The Tet Offensive of January-February 1968, in which North Vietnamese and Viet Cong forces launched coordinated attacks on more than 100 South Vietnamese cities and towns, marked a major shift in American public opinion despite resulting in a military defeat for the attackers. President Nixon began withdrawing troops in 1969 while simultaneously expanding bombing campaigns into Cambodia and Laos. The Paris Peace Accords of January 1973 resulted in American withdrawal. Fighting between North and South Vietnam continued until the fall of Saigon on 30 April 1975.

Estimates of total deaths vary considerably depending on methodology and source. American military deaths are documented at approximately 58,200. South Vietnamese military deaths are estimated at over 200,000. North Vietnamese and Viet Cong military deaths are estimated between 400,000 and 1.1 million, a range reflecting significant methodological disagreement among demographers. Civilian deaths across Vietnam are estimated in the hundreds of thousands to over two million. The war produced millions of refugees, widespread environmental damage from defoliant use (particularly Agent Orange), and long-term health consequences for veterans and Vietnamese civilians alike. The United States did not achieve its stated objective of preserving an independent, non-communist South Vietnam. Vietnam was reunified under the Socialist Republic of Vietnam in 1976. The war contributed to significant political and cultural upheaval in the United States, including the erosion of public trust in government, the collapse of the military draft, and lasting divisions over American foreign policy. See Vietnam War - History for a full historical account.

There is broad historical and scholarly consensus on the basic chronology and documented facts of the war, including troop numbers, major engagements, and the outcome. Significant interpretive disagreement exists on questions of strategic decision-making, the morality and legality of various military actions, the reliability of casualty estimates, and the lessons the war holds for American foreign policy. There is no single authoritative consensus page for this topic; relevant scholarly findings are noted under individual subtopics where applicable.

Antiwar and Moral Opposition - Opponents of the war, including some veterans, argued that the conduct of the war - including civilian casualties, use of chemical defoliants, and the strategic bombing of North Vietnam - constituted moral and legal violations regardless of geopolitical justifications. Read this viewpoint

Containment and Strategic Necessity - Some analysts and historians argue that American intervention was a reasonable application of containment doctrine and that different strategic or political decisions could have achieved a better outcome. Read this viewpoint

Unjust and Unwinnable Intervention - A contrary view holds that the war was fundamentally misconceived, that South Vietnam lacked the political legitimacy and popular support necessary to survive, and that American intervention prolonged suffering without altering the inevitable outcome. Read this viewpoint

Winnable War, Lost at Home - Some military analysts and commentators argue that the war was militarily winnable but was undermined by political constraints, media coverage, and domestic opposition. Read this viewpoint

• Vietnam War - History
• Vietnam War - Debate
• Cold War
• Domino Theory
• Gulf of Tonkin Incident
• Vietnam War Veterans
• Agent Orange
• Tet Offensive
• Paris Peace Accords
• Vietnam War and U.S. Foreign Policy - Consensus

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2. Karnow, Stanley. Vietnam: A History. Viking, 1983.
3. Moyar, Mark. Triumph Forsaken: The Vietnam War, 1954-1965. Cambridge University Press, 2006.
4. Turley, William S. The Second Indochina War: A Concise Political and Military History. 2nd ed. Rowman & Littlefield, 2009.
5. Lewy, Guenter. America in Vietnam. Oxford University Press, 1978.
6. Ellsberg, Daniel. Secrets: A Memoir of Vietnam and the Pentagon Papers. Viking, 2002.
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8. U.S. Department of Defense. Selected Manpower Statistics. Washington, D.C., 1985.
9. McNamara, Robert S. In Retrospect: The Tragedy and Lessons of Vietnam. Times Books, 1995.
10. Kissinger, Henry. Ending the Vietnam War: A History of America's Involvement in and Extrication from the Vietnam War. Simon & Schuster, 2003.