ABSOLUTE LIE!
The civilian government of the USA and the Lying Media defeated the USA. It was NOT the Military. The civilians grew weary and surrendered just like now. Except now, the acting commander in chief is BOUGHT by the Communist.
Worth repeating. The 20's something author is professionally negligent, if not intentionally deceptive.
For the benefit of young FR readers:
The U.S. defeated the enemy combat forces and North VN was no longer able to field and army.
Thereafter the warring parties and the U.S. signed a peace treaty.
1972 The U.S. left VN at its convenience.
The Dem majority in Congress discontinued military aid for South VN with knowledge the North was building an oversized military force.
1975 The North invaded South VN.
The ladder to the embassy rooftop for escape helicopters was not for U.S. military but for Vietnamese that had been associated with the U.S. (see today's Afghanistan)
How do those facts align with what you were taught in high school and college?