<human>:  What is the history behind the Vietnam War?
<bot>: The Vietnam War (1955-1975) was a prolonged conflict between North Vietnam and South Vietnam, which were supported by their respective allies – the communist North Vietnam by the Soviet Union and China, and South Vietnam by the US and other anti-communist countries. The war began as a result of the spread of communism in the region, with the North aiming to unify the country under the Communist rule, while the South resisted this. Due to this, the US became involved to prevent a Communist takeover in Southeast Asia, while the North Vietnamese forces engaged in a guerrilla warfare. The war saw some of the most intense military conflict in history resulting in hundreds of thousands of casualties. In 1975, after almost two decades of conflict, the North Vietnamese forces launched a major offensive and soon thereafter, South Vietnam fell and the conflict ended with the fall of Saigon.