The US involvement in Vietnam was originally aimed to contain
communist China because the US government was convinced that communist
China had the plan to expand its border and influence to as far as
Indonesia and Singapore. In the 1950s and 1960s, it had seen local
communist ethnic Chinese tried but failed to "liberate" Malaysia and
Indonesia.
However, IMO US involvement in the Vietnam war in 1964 was premature.
The war was still ran by small guerilla groups and the US did not have
enough hard evidence to convince the American public that the
communist block actually invaded South Vietnam. Later in 1965 the US
Navy had to fabricate the Tonkin Bay incident in which North
Vietnamsese Navy was accused to attack US Navy ships in North Vietnam
to expand the war. Because Hanoi denied the incident ever existed,
American public was not convinced that US troops were needed to
protect South Vietnam from communist expansion.
Because US troops were well trained in conventional war but were not
in guerrilla welfare, Hanoi ran the guerrilla warfare against the US,
not to win but to bother the American public enough so that US troops
had to leave South Vietnam. This is similar to the tactics used by a
group of hayenas that harrased the lions for the killed deer. The
lions eventually gave up walk away and let the hayenas help themselves
with the deer.
After US troops left Vietnam in 1973, communist block launched massive
conventional warfare against South Vietnamese positions. They tested
the US reaction by having NVA troops attacked Phuoc Long, Ban Me Thout
and Chinese troops invaded Paracell chain of Islands in South China
Sea. After knowing that the US abandoned its containment of communist
policy, Hanoi launched the final massive invasion in 1975. Knowing
that the US dropped its committment to stop communist invasion in
Asia, South Vietnamese government arranged the transition of power to
a neutral group lead by Gen. Duong van Minh who surrendered on April
30 1975.
The US should have waited until China and North Vietnam launched the
massive invasion on South Vietnam to send troops to Vietnam. It did
not wait and lost the support from its people. In 1975 when China
publicly invaded South Vietnam, the US was contained by its congress
and had to declare that IndoChina was no longer important to US
security to save face.
Ironically, US as the nation who agressively acted to contain
communist in Asia was later contained in its own land. The supposed to
be contained nations, China and North Vietnam, was set free to invade
other nations during the period of 1973-1980.
Lessons learned: Premature involvement backfired.