The US effectively lost the war before it even started. They decided to support the French during their colonial war due to the so-called 'domino theory,' which

The US effectively lost the war before it even started. They decided to support the French during their colonial war due to the so-called 'domino theory,' which ignored the fact that the Vietnamese hated or feared China more than anyone else. After the French were gone, China would have been the biggest geopolitical threat to Vietnam. If the right choices had been made in the 1940s and early 1950s, it wouldn't have been that hard to turn Vietnam into an East Asian equivalent of Yugoslavia, if not an actual US ally