In context of the time, it made sense to protect South Vietnam from falling to Communist invasion. It had been done successfully in Korea. Laos became communist, so did Cambodia, and Thailand fought communist rebels in the north for many years, so the Domino Theory did have merit.
However, a major difference with Korea were the borders, Korea only had China to the North, but South Vietnam had long borders with Laos and Cambodia stretching the entirety of the country, with which the communists could infiltrate the territory with their own people and weapons. So the war became a counter-insurgency within South Vietnam as well as an invasion from the North with conventional forces.
The only way to win would have been to bomb North Vietnam without limits WW2 style. The US did drop an immense amount of bombs, but they were still limited to specific targets and designated regions, not on the entire country.
"Over the course of the two decades the US military was in Vietnam, the US dropped an estimated 5 million tons of explosives. That’s twice as much as during the entirety of World War II, and it remains, to this day, the largest bombardment of any single country ever."
SourceProbably the only thing that could have stopped North Vietnam would have been a full out invasion of North Vietnam, Laos and Cambodia. They couldn't have done that due to the (perceived?) threat of nuclear war with China.
The whole thing was a clusterfuck of epic proportions. The craziness never ended. You had
1) A president who had no idea or experience of foreign relations/geopolitics (Johnson)
2) An autistic genius with a love for statistics and "system analysis" who was the main drive behind bodycount (McNamara)
3) A general in charge widely believed to have been a moron or in any case unable to adapt to an insurgency style war (Westmoreland)
I read something that struck me on reddit once, that these were the idiots Von Clausewitz wrote about in "On War".
What else could it have been other than a clusterfuck?
Strategic Hamlet Program (essentially refugee/concentration camps)
M-16 rifle (so prone to jamming when it was introduced, it was more dangerous to US soldiers than the actual enemy)
18 year old kids sent into the jungle in full combat gear to search for an enemy who could hear them from a mile away.
Combat tours limited to one year (by the time the grunts knew what they were doing it was time to go)
Draft that affected only the poor (National Guard/university students and anyone with enough money to pay a doctor, like Donald Trump with his bone spurs, got a deferment)
Project 100,000 aka McNamara's folly (the lowering of standards, allowing 80 IQ Hankins-type soldiers to be recruited and sent to battle where they were turned into mincemeat)
Rainbow herbicides (5,000,000 Vietnamese exposed to Agent Orange, vast tracts of forest/jungle affected, ecological disaster)
Decades later McNamara (who before he was fired by Johnson, had secretly turned against the war and had a mental breakdown) admitted that "we were wrong, terribly wrong".
