For much of Vietnam's history it has been under foreign rule, primarily by the Chinese.
In 1860, France began its domination of the area and had, by the late 19th century,
implemented its colonization in a number of regions around the Gulf of Tonkin. During WWII,
the Japanese government took control of much of the area and set up a puppet regime that was eventually forced out by the Vietnamese at the end of that war in 1945.

After WWII and until 1955, France fought hard to regain their former territories in the region,
but with a poorly organized army and little determination among the troops, their efforts soon
collapsed. The French were finally defeated at Dien Bien Phu on the 8th of May 1954 by the
communist general Vo Nguyen Giap. The French troops withdrew, leaving a buffer zone separating the North and South and set up elections in order to form a government in the South.
The communist regime set up its headquarters in Hanoi under the leadership of Ho Chi Minh.
Many North Vietnamese left the country and fled south where the self-proclaimed president,
Ngo Dinh Diem had formed the Republic of Vietnam.

Fearing a communist takeover of the entire region, the United States grew more and more wary of the progress of Ho Chi Minh and the Vietcong. Communism had become the evil menace in the United States and with expansion of Soviet rule into Eastern Europe, Korea and Cuba, the Americans were bent on stopping communism from spreading any further.

With the cold war at its height, the US leaders were worried that an attack on North Vietnam by the US would create tensions with the Chinese and Russians that would, in turn, lead to a larger conflict and possibly WW III. This created a difficult situation for the US and would eventually lead to many internal conflicts, which ultimately prevented the US from forming a firm policy for the region. The US was also faced with a number of cultural differences between the two countries, and what was considered corrupt by the US government was considered legitimate by South Vietnamese standards. It was difficult for the US to portray South Vietnam as a hard working, hard fighting democracy; corruption was widespread among officials and the armed forces. The Army of the Republic of Vietnam (ARVN) was disorganized due to the low morale of it's leaders and their singular interest in personal gain. Therefore the US had a great deal of difficulty in holding the army together in South Vietnam and saw only one solution, that was to start taking care of things for themselves. By 1950 the US began sending their first troops, firstly in an advisory role, which slowly escalated into a full blown commitment.

The large-scale involvement of the US came under the tenure of President Lyndon B. Johnson and his Gulf of Tonkin Resolution. Johnson had replaced John F. Kennedy after he was assassinated in Dallas, Texas 1963. As president, he was torn between the differing strategies the US had for Vietnam. The increasing involvement and the escalation of troop involvement meant there were more casualties and more problems at home. But Johnson, who was always concerned about his image, and as president, held the power to halt the war in Vietnam, could not face the thought of being regarded as the first president in US history to loose a war. The pressure around him grew so intense, that he was only left with one option and that was not to run for a second term.
Basically, he handed the hot potato to Richard M. Nixon.

The escalation of the war continued during the Nixon years. The top US commander in Vietnam was General William Westmoreland; he had to face an army full of young men placed in an environment that was totally alien to them. There was no clear front to the conflict and basically, the enemy could be hiding anywhere and everywhere. Life in the jungle was tortuous and there were no home comforts. Drugs and other stimulants filtered their way into the daily routine of many servicemen and morale quickly started to fall. (In 1969, a Defense Department study showed that 20 percent of US soldiers in Vietnam were using marijuana either occasionally or frequently. By 1969, military police were arresting 1,000 soldiers per week for possession.
Heroin use also spread within a small group of soldiers and was readily available for only
2-3 dollars per dose. Drug urine analysis tests were performed on some soldiers before returning home. However, the majority of the soldiers did not use drugs as popular myth may suggest).
For the first time, people in the US resisting the draft were given acceptance although still not by the majority of citizens. Riots and demonstrations against the war became the norm in the US, with numerous veterans taking part in the efforts to stop the war, strengthening the issue.

Finally, the US government saw that it was in a no-win situation and began making plans to withdraw.