The American intervention in Vietnam is considered by the whole world to be America's greatest loss and longest war. Before the Vietnam War began, the idea of ​​the United States losing that war was unheard of, because America was technologically superior and no country in Southeast Asia could compete with them. Lyndon B. Johnson announced that he would not be the president who would allow Southeast Asia to become communist. Why the United States lost the war has been the subject of extensive debate since the war's end, as many factors influenced the reason for this defeat; the war was a political loss, having lost support not only from the American public but also from the South Vietnamese and having lost a political mandate for the war in 1973, when the last American soldier left; they lost militarily, failing to achieve their basic objectives, underestimating North Vietnamese tactics, and economically spending $20 billion a year on the war, causing a failure of social reform. This mission will focus on those fundamental factors that are considered the reason for the defeat of the United States in Vietnam. Politically, the United States failed in this matter. Although Lyndon B. Johnson's presidential election gave his administration public support for the strong stance he would take. The government eventually lost popular support, due to the atrocities in Vietnam, which were shown to the world through the media showing the aftermath of Operation Rolling Thunder. At the height of the war, America was losing 300 soldiers a week, which also caused outrage within America since almost everyone had lost a relative or friend. During the presidency of Lyndon B. Johnson, anti-war movements became popular among young people, protests and sit-ins... middle of newspaper ...... communist; 1975 also saw Laos and Cambodia become communist. The result helped the United States seek a new policy toward the Cold War. In conclusion, the United States lost the Vietnam War for many different reasons, all of which were important in contributing to the inevitable defeat. The main reason why the United States lost the war was internal division and loss of support from the people of not only America and Vietnam, but the entire world. Works Cited Anderson, David, The Vietnam War (Longman, New York; 2005) CB Jones, Understanding the Cold War (Bookpoint Ltd, London; 2010)Anderson, David L. The Columbia Guide to the Vietnam War (Columbia University Press, New York; 2002)Hess, Garry R. Vietnam: Explaining America's Lost War (Blackwell Publishing, Oxford; 2009) Roberts, Pricilla, The Cold War (Sutton Publishing, Stroud; 2000