Forgive my ignorance.
Why is 1971 significant?
To be fair most Americans by then recognized that this had been a "no win" war. At least in Korea the North Koreans and Chinese were pushed out of South Korea. Just a few years before that W.W.II ended with unconditional surrender by all of our enemies. From the beginning our "best and brightest" leaders' no-win, graduated response methods failed at the cost of far, far too many lives. The American public had been snookered.
Nothing special happened in 1971, 1968 would have been better but it would have required really bold action. The North was astounded that the American press reported that the Tet offensive was their victory. It encouraged them to continue. After the war the American press won the praise of General Giap as his most valuable guerilla.
After four solid years of major combat here was a chance to end the war by winning all the battles. Instead the military was attacked by the left as incapable of winning -- which, of course, is what the left wanted. Had the military acted then the war could have ended, the New Left would have been destroyed and they would not control so much of our society including the once great Democrat party. IMO.
I can't resist, sorry. Nothing personal. But I've seen others say that a mind that opens as a parachute risks having the brains fall out. :>)