Thanks for your informed and interesting comment!
This is an interesting position, though I think it suffers from the same shortcuts that much US thinking does when it tries to grapple with prior arrangements that seem inconvenient today because of changing strategic context.
To what extent did it contribute to the fall of the Soviet Union? An incredible amount. China blocked the Soviet Union in all of South Asia, it abstained from diplomatic support - it wielded both its position on the UNSC and it's nuclear capability to check USSR. Then, it challenged the central tenets of Communism specifying that it had a different interpretation closer to the original theory - thus challenging the centrality of Russia ideologically. China's withdrawl represented approximately a third of the world population removing itself from the union: the concept of "domino theory" at the time described - in a certain pop science way - how states arriving into and dropping out of the union had a chain reaction effect. Since the alliance with China, the Cold War no longer was fought in the Asian theatre - closing down an entire continent of front to the war. The rest of the Cold War would be fought in Central Asia (and eventually in the Middle East), and in Europe.
Of course, the United States knew from very early that it was going to lose in Vietnam: the Pentagon Papers discussed this in great detail. The United States was there on a cost imposition exercise. The result it found in the alliance with China was a mutually satisfactory way to close the conflict. In this regard China didn't win the Vietnam war either.
> The various potential military hotspots – Vietnam, the Korean peninsula, the South China Sea – would probably be in much the same state if the US-China deal never happened.
I have no idea. That's 60 years of alternative history to imagine. Fascinating, but not clear.
> Many people say that Nixon's decision was a great strategic move, but I am unconvinced – the US got some short-term assistance against the Soviets which it didn't really need and didn't make much difference anyway; in exchange, the US put itself in a weaker strategic position vis-à-vis China for many decades to come.
This seems to be a rising opinion in the National Security Core of the United States, and also seems to be the take of the new Trump Administration.
Personally I see this as historical revisionism, contextualized by modern concerns over historical accuracy.
I fully agree that China and it's potential rise are considered by the National Security State of the American Government to be a dark horse scenario, and a greater potential spoiler to American hegemony than Russia (a waning power) today.
I understand how someone could mistake the situation we are in today with a security outlook at China's rise and want to throw out some of the alliance concessions because in this day and age they are inconvenient. We've seen that before in history (indeed, in American history) and so it's congruent with the kind of behavior we would expect.
> China's economic development since the 1980s has provided many economic benefits to the US and its allies. But, that still could have happened even if there was a more assertive US policy towards PRC
I think all of this is very accurate, provided there was _some_ deal to get an alliance. Had it been possible for the United States to do that without recognizing PRC, I serious doubt. But yeah, if that had been possible, I think much of the geoeconomic situation would have looked the same.