The 'One China' policy essentially is about saving face. China is extremely sensitive to not being seen as losing face because of bullying from the West about what they consider to be their sphere of influence.
That in practice Taiwan acts and to all intents and purposes is an independent country doesn't matter as much as being able to claim that Taiwan is a republic of China does.
So, if everybody would just pretend that the 'One China' view is the correct one while Taiwan gets away with being a relatively progressive democratic society everybody wins.
If Trump starts throwing his weight around he might just trigger an invasion of Taiwan and just like Europe and the USA stood by while the Eastern part of Ukraine was annexed I do not expect anybody to lift a finger to stop it.
That's why you don't put unstable bullies in charge of foreign diplomacy with your single largest trading partner and a formidable military power to boot.
Vastly oversimplified but that's about the gist of it as far as I can see, corrections welcome.
And it might not be the only possible scenario - in fact, with all the Hitler comparisons floating around, this stance towards China reminds me a lot of the appeasement politics towards Hitler.
Ultimately, saving face with regard to Taiwan is probably just one part of the general trade deal with China? So as the other parts, it should probably be up for negotiation? Or even be a factor ("we pretend Taiwan belong to you, and you give us moar iPhones").
Not saying that protectionism is a good idea, but also not saying that all trade deals are always optimal for both parties.
I think Ukraine was about more than saving face for Russia, too - Russia has always wanted the Krim for strategical reasons?
That's pretty much the way it was. Except for it being a lot more than just iPhones.
> I think Ukraine was about more than saving face for Russia, too - Russia has always wanted the Krim for strategical reasons?
The Krim is extremely important from a military perspective to Russia, their response was - again - extremely predictable (in fact, I'm surprised they didn't simply call the EU's bluff and invaded outright but then again, appearances matter even to the Kremlin).
See also: Kaliningrad.