The Vietnam War was the longest military conflict in U.S. history. The hostilities in Vietnam, Laos, and Cambodia claimed the lives of more than 58,000 Americans. Another 304,000 were wounded. The main military organizations involved in the war were, on the side of the South, the Army of the Republic of Vietnam (ARVN) and the U.S. military, and, on the side of the North, the Vietnam People's Army (VPA), also known as the North Vietnamese Army (NVA) also called the People's Army of Vietnam (PAVN), and the Vietcong , or National Front for the Liberation of South Vietnam (NLF), a communist army based in the South.
From 1946 until 1954, the Vietnamese had struggled for their independence from France during the First Indochina War. At the end of this war, the country was temporarily divided into North and South Vietnam. North Vietnam came under the control of the Vietnamese Communists who had opposed France and who aimed for a unified Vietnam under Communist rule. The South was controlled by Vietnamese who had collaborated with the French. In 1965 the United States sent in troops to prevent the South Vietnamese government from collapsing. The United States entered the war to prevent a communist takeover of South Vietnam as part of their wider strategy of containment.Ultimately, however, the United States failed to achieve its goal, and in 1975 Vietnam was reunified under Communist control; in 1976 it officially became the Socialist Republic of Vietnam. During the conflict, approximately 3 to 4 million Vietnamese on both sides were killed, in addition to another 1.5 to 2 million Lao and Cambodians who were drawn into the war.

Post war

The United States also paid a high political cost for the Vietnam War. It weakened public faith in government, and in the honesty and competence of its leaders. Indeed, skepticism, if not cynicism, and a high degree of suspicion of and distrust toward authority of all kind characterized the views of an increasing number of Americans in the wake of the war. The military, especially, was discredited for years. It would gradually rebound to become once again one of the most highly esteemed organizations in the United States. In the main, however, as never before, Americans after the Vietnam War neither respected nor trusted public institutions. A new consensus among foreign policy makers, reflecting the lessons learned from the Vietnam War, became manifest: the United States should use military force only as a last resort; only where the national interest is clearly involved; only when there is strong public support; and only in the likelihood of a relatively quick, inexpensive victory.
 
Reference Links:
http://www.english.illinois.edu/MAPS/vietnam/vietnamwar.htm
http://en.wikipedia.org/wiki/Vietnam_war#Opposition_to_the_Vietnam_War:_1962-1975