The US was bolstering the Corrupt South Vietnamese government from being replaced democratically by a communist government. They did this because they wanted a base for a strategic navy presence in the area.
It began by helping the French after WWII and moved on to protecting the world against communism.
neither UN or NATO took part in Vietnam
US Army Chief of Staff and US Ambassador to South Vietnam.
South Vietnam was already a sovereign nation by the time the US entered the nation. Its title was the "Republic of South Vietnam."
Part of the cold war.
Part of the cold war.
All of it.
Vietnam is a war which the US definitely lost because the goal of the war was to support the Republic of Vietnam (aka South Vietnam) and prevent it from falling to the Democratic Republic of Vietnam (aka North Vietnam). Despite massive effort and sacrifice on the part of the US, South Vietnam collapsed in 1975.
To fight communism; part of the cold war.
Containment .
Part of the cold war.
The Northern Communist part of Vietnam came out victorious, they declared Independance and even to this day they could still be partly Communist