Claim: The United States entered into the Vietnam War to prevent communist takeover of South Vietnam.

The Vietnam War -LRB- Chiến tranh Việt Nam -RRB- , also known as the Second Indochina War , and known in Vietnam as Resistance War Against America -LRB- Kháng chiến chống Mỹ -RRB- or simply the American War , was a war that occurred in Vietnam , Laos , and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975 . It was the second of the Indochina Wars and was officially fought between North Vietnam and the government of South Vietnam . The North Vietnamese army was supported by the Soviet Union , China and other communist allies and the South Vietnamese army was supported by the United States , South Korea , Australia , Thailand and other anti-communist allies . The war is therefore considered a Cold War-era proxy war .   The Viet Cong -LRB- also known as the National Liberation Front , or NLF -RRB- , a South Vietnamese communist common front aided by the North , fought a guerrilla war against anti-communist forces in the region , while the People 's Army of Vietnam , also known as the North Vietnamese Army -LRB- NVA -RRB- , engaged in more conventional warfare , at times committing large units to battle . As the war continued , the military actions of the Viet Cong decreased as the role and engagement of the NVA grew . 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 . In the course of the war , the U.S. conducted a large-scale strategic bombing campaign against North Vietnam .   The North Vietnamese government and the Viet Cong were fighting to reunify Vietnam . They viewed the conflict as a colonial war and a continuation of the First Indochina War against forces from France and later on the United States . The U.S. government viewed its involvement in the war as a way to prevent a communist takeover of South Vietnam . This was part of the domino theory of a wider containment policy , with the stated aim of stopping the spread of communism worldwide .   Beginning in 1950 , American military advisors arrived in what was then French Indochina.The Military Assistance Advisory Group , Indochina -LRB- with an authorized strength of 128 men -RRB- was set up in September 1950 with a mission to oversee the use and distribution of US military equipment by the French and their allies . U.S. involvement escalated in the early 1960s , with troop levels tripling in 1961 and again in 1962 . U.S. involvement escalated further following the 1964 Gulf of Tonkin incident , in which a U.S. destroyer clashed with North Vietnamese fast attack craft , which was followed by the Gulf of Tonkin Resolution , which gave the U.S. president authorization to increase U.S. military presence . Regular U.S. combat units were deployed beginning in 1965 . Operations crossed international borders : bordering areas of Laos and Cambodia were heavily bombed by U.S. forces as American involvement in the war peaked in 1968 , the same year that the communist side launched the Tet Offensive . The Tet Offensive failed in its goal of overthrowing the South Vietnamese government , but became the turning point in the war , as it persuaded a large segment of the U.S. population that its government 's claims of progress toward winning the war were illusory despite many years of massive U.S. military aid to South Vietnam .   Gradual withdrawal of U.S. ground forces began as part of `` Vietnamization '' , which aimed to end American involvement in the war while transferring the task of fighting the communists to the South Vietnamese themselves . Despite the Paris Peace Accord , which was signed by all parties in January 1973 , the fighting continued . In the U.S. and the Western world , a large anti-Vietnam War movement developed as part of a larger counterculture . The war changed the dynamics between the Eastern and Western Blocs , and altered North -- South relations .   Direct U.S. military involvement ended on 15 August 1973 . The capture of Saigon by the North Vietnamese Army in April 1975 marked the end of the war , and North and South Vietnam were reunified the following year . The war exacted a huge human cost in terms of fatalities -LRB- see Vietnam War casualties -RRB- . Estimates of the number of Vietnamese soldiers and civilians killed vary from 966,000 to 3.8 million . Some 240,000 -- 300,000 Cambodians , 20,000 -- 62,000 Laotians , and 58,220 U.S. service members also died in the conflict , and a further 1,626 remain missing in action .