We accomplsied our political objective, as well as our tactical and strategic objective. We forced the North to agree to stay out of South Vietnam. To say that we were defeated in Vietnam, because the North crossed into South Vietnam, after we left is to say that the Allies lost WW1, because Hitler rebuilt the German Army and invaded Poland.
The problem is, Americans have heard it repeated so many times, "The US lost the Vietnam War", that they refuse to look at the actual facts and realize that we didn't. As far as the Lefties and the anti-war folks go, they either can't admit that they're totally wrong, or they won't admit they're totally wrong, because the, "we lost", narrative takes away from the, "we shouldn't have been there", mantra that is constantly parroted. They are obligated to root for American failure. The same thing will happen with Iraq and Afghanistan.
Quote who you want: Yingling, Clausewitz, Smith, Hart, you name it. The one thing their theories and philosophies can't replace, is historical fact. The one major fact remains, The United States didn't lose the war in Vietnam. If you think I'm wrong, stop posting opinions and philosophies and start posting historical events that prove me wrong.
Ever hear of the Paris Accords?