China | Taiwan
involved: china, taiwan, hong kong, united states
The Chinese, despite having a reputation for opacity, are in fact quite meticulous in announcing their big moves well ahead of time, as they did with Hong Kong.
Thanks to Huawei and the trade wars, the retaking of Taiwan has now moved inside the Overton window of PRC policymaking: we're no longer hearing open-ended rhetorical proclamations of "one China" at party conferences; we're deep into think-tank debates and policy papers about cost-benefit analysis for Chinese supply chains (control of Taiwan Semiconductor would spare China from having to attempt a Manhattan-project-sized 2-10 year struggle to reach those levels of precision on their own).
I also sense the loose beginnings of an explicit timeline — "within Xi Jinping's term", which is in theory could mean his lifetime, but I think when people say that sort of thing they tend to mean five years.
I'm persuaded that the Chinese could explain away the Hong Kong debacle to Taiwan's satisfaction: It is a tragic truth that China did stick to its hands-off promises in the Basic Law (well 90% of them at any rate), and that Hong Kong was doing very well after 1997, until Hong Kong itself revolted, provoked largely by the stupidity and incompetence of its own local government. I'm not trying to mitigate the tragedy of Hong Kong here, just to say I think China could successfully rationalise its behaviour in talks with the Taiwanese.
I doubt anybody now thinks America would go nuclear against China on behalf of Taiwan; so, in a sense, the military bit is already over, since China would certainly be the better bluffer. Even in conventional weaponry I doubt the Americans would dare to fight inside the Taiwan Straits; they'd be lobbing stuff in from Okinawa.
We might then have a stand-off akin to a Cuban missile crisis, but nothing the Chinese couldn't escalate by dropping a small nuclear weapon on a US Antarctic base or unpersonned atoll or something, just as proof of concept.
So, all told, I can see the way to a Hong Kong-style autonomy deal for Taiwan which is acceptable to the Taiwanese. The sting in the tail for the Americans would be that their help would not even be wanted. And, after which, America would face a far more formidable China, once Taiwan with all its technology and weaponry had been integrated.