@Hoss @p @istvan @lanodan @hj @ProfessionalPetFoodTaster @gentoobro @mangeurdenuage Except that's not how it played out at all:
"there were possible avenues to achieve diplomatic victory [in Vietnam] before ever needing to put boots on the ground"
With Communists? Supported by the Evil Empire? We don't live in the same universe.
JFK also took a different tack, assassinating the two fellow Diem bothers, the Catholic strongmen who ran the south. Only fitting he was in turn assassinated a month later, and of course that seriously destabilized the South, and it was years before they were ready to trust us again. More fools them, or as Kissinger put it right after Nixon was elected in 1968 but before he was in office:
"Nixon should be told that it is probably an objective of [Clark] Clifford to depose Thieu before Nixon is inaugurated. Word should be gotten to Nixon that if Thieu meets the same fate as Diem, the word will go out to the nations of the world that it may be dangerous to be America's enemy, but to be America's friend is fatal."
"leadership in the north was actually getting ready to sue for peace after the Tet Offensive failed. But before they could do that, they saw we were withdrawing and could practically walk on in and seize the south."
Again, your faith in negotiating with Communists is touching. But Vietnamization worked well enough, and was put to the acid test by the 1972 Easter Offensive. The Soviet's second supply of a full mechanized army for the NVA PVAN, with 150K men (300K per Wikipedia) was utterly smashed, with 40K considered themselves to be lucky to make it back north.
The first really major use of smart weapons, bombs in this case dropped by the US (I remember hearing/reading about this in real time), preceding the Yom Kippur War a year later (primitive ATGMs plus SA-6 SAMs hurt the IDF badly, and Nixon's resupply of aircraft prompted the Arab oil embargo...).
Your blessed diplomacy? There was a treaty signed in January 27, 1973. Hmmm, Wikipedia says "fighting between the three remaining powers temporarily stopped for less than a day...."
Although the North did keep some of the territory they'd seized, but the real end was all too simple in principle: Soviets supply a third army's worth of equipment, which we now realize helped to bankrupt them, the Congressional Watergate Committee was established eleven days later and that eventually gave the politicians on the side of World Communism a veto power to arrange an all around surrender, like ending our ABM defenses in early 1976.
Before then, the South was deliberately starved of munitions, and I'd assume spare parts for their fighter jets (the infamous naked burned girl came from a South Vietnamese air strike), the individual infantryman had one grenade and less than a normal basic load of rifle rounds (or so was said at the time and long after). And of course no US air support as was needed to stop the 1973 invasion.
But in a different world ... maybe the North would have tried another gambit. Maybe they would have tried again and been even more comprehensively stomped with a couple more years of weapons development. But like Afghanistan a political failure, just not one doomed from the start.
Better culture, enabled by much higher IQs; like their fellow Arabs surrounding Israel, Afghans are about as dumb as African-Americans, it could have worked. But the New Left was firmly on the other side and they succeeded in taking over the Democratic party between Nixon's two successful elections, 1968 and 1972. Something Reagan had to fight, and we can circle back to Afghanistan for part of that, Carter was characteristically completely shocked by the Soviet invasion of it, and responded ineffectually, plus pissed off everyone with a grain embargo.