Let me offer another perspective from my personal observations directly after we pulled out of Vietnam.
I served a tour there in the Army from 70-71.
After the war, in August of 1974, I went back to Vietnam as a government contractor with Lear-Siegler in an effort to teach the S. Vietnamese military how to take care of and maintain the immense amount of aircraft that we left with them, as part of Nixon’s “Vietnamization” program.
This was at Tan Son Nhut AFB, and between classroom and flightline instruction that I gave to S. Vietnamese military personnel, it was obvious to me by their ho-hum attitudes and lack of motivation to learn, that they didn’t want to have anything more to do with the war and they knew S. Vietnam was in the process of falling to the North’s southward march.
Everyday I would see numerous cargo planes landing and off-loading hundreds of dead S. Vietnamese solders, and my students saw it too.
I won’t watch the Burn’s documentary and don’t know if he’ll touch on the “Vietnamization” effort that America undertook, but from my perspective, I knew during the Summer of ‘74 that it was a losing effort, and 8 months later S. Vietnam fell to the Communists.