The Vietnam War was a Cold War-era military conflict that occurred in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975. This war followed the First Indochina War and was fought between North Vietnam, supported by its communist allies, and the government of South Vietnam, supported by the United States and other anti-communist countries. The Viet Cong (also known as the National Liberation Front, or NLF), a lightly armed South Vietnamese communist-controlled common front, largely fought a guerrilla war against anti-communist forces in the region. The Vietnam People's Army (North Vietnamese Army) engaged in a more conventional war, at times committing large units into battle. U.S. and South Vietnamese forces relied on air superiority and overwhelming firepower to conduct search and destroy operations, involving ground forces, artillery, and airstrikes.

The U.S. government viewed involvement in the war as a way to prevent a communist takeover of South Vietnam as part of their wider strategy of containment. The North Vietnamese government and Viet Cong viewed the conflict as a colonial war, fought initially against France, backed by the U.S., and later against South Vietnam, which it regarded as a U.S. puppet state. American military advisors arrived in what was then French Indochina beginning in 1950. U.S. involvement escalated in the early 1960s, with troop levels tripling in 1961 and tripling again in 1962. U.S. combat units were deployed beginning in 1965. Operations spanned international borders, with Laos and Cambodia heavily bombed. American involvement in the war peaked in 1968, at the time of the Tet Offensive. After this, U.S. ground forces were gradually withdrawn as part of a policy known as Vietnamization. Despite the Paris Peace Accords, signed by all parties in January 1973, fighting continued.

Vietnam ( listen), formally the Socialist Republic of Vietnam (Cộng hòa xã hội chủ nghĩa Việt Nam;  listen), is the easternmost country on the Indochina Peninsula in Southeast Asia. With an estimated 91.5 million inhabitants as of 2012, it is the world's 13th-most-populous country, and the eighth-most-populous Asian country. The name Vietnam translates as "South Viet", and was officially adopted in 1945. The country is bordered by China to the north, Laos to the northwest, Cambodia to the southwest, and the South China Sea to the east.

The Vietnamese became independent from Imperial China in 938 AD, following the Battle of Bạch Đằng River. Successive Vietnamese royal dynasties flourished as the nation expanded geographically and politically into Southeast Asia, until the Indochina Peninsula was colonized by the French in the mid-19th century. The First Indochina War eventually led to the expulsion of the French in 1954, leaving Vietnam divided politically into two states, North and South Vietnam. Conflict between the two sides intensified, with heavy foreign intervention, during the Vietnam War, which ended with a North Vietnamese victory in 1975.