Johnson said he wouldn't run to be re-elected. Martin Luther King Jr and Robert Kennedy were both murdered.
It is not really "who ended the Vietnam war?" but "how did the Vietnam war end?" in which case i do not have the answer too.
The known POW's from the Hanoi Hilton complex left around 1973. There are several hundred missing, and it's not known if any of the missing are still alive.
There was no "third of the fifth cavalry DIVISION" in Vietnam. Not a U.S. outfit at least. There was a 3rd Squadron, 5th U.S. Cavalry assigned to the 9th Infantry Division in Military Region III (MR-3) or (MR-4) near the Mekong Delta, which was OPCON or attached to the U.S. Army's 1st Brigade 5th Mechanized Infantry Division up in MR-1, commonly called "I" Corps, just below the DMZ.
A wide variety of Australians were against Australia's involvement in the Vietnam war, especially young Australians, who were being conscripted to help The USA bolster an unpopular government in Vietnam for strategic reasons.