Not to argue with this (or anything else in your message), but to ask a question (to which I've never, in many decades, gotten a straight answer):
At the time of the Vietnam War, that whole area had a complex, messy history involving lots of colonial and foreign involvement, as a result of which Vietnam ended up divided. Vietnam had once been and should have again become a single country; but it was in fact divided into two de facto countries, each with de facto but more or less functioning and more or less legitimate (and more or, generally, less admirable) governments.
The Vietnam War then resulted, not because the North Vietnam government was threatened with invasion by the U.S., but because the NV government was simply determined to obtain sovereignty and control over South Vietnam, and to do so initiated an aggressive (and quite vicious) war to do this -- right? (And were willing to commit genocide on their own citizenry to accomplish this, not so?)
The U.S. of course then got involved on the South Vietnam side, which it perhaps should and more likely should not have done. The initial aggression by North Vietnam was, however, in *either* case, clearly illegal -- right? It may not have justified our involvement, or our conduct once involved, but it *was* illegal on their part and deserved international condemnation, not so?