I might be a hopeless optimist, but I don't think a USN/USAF/USMC vs PLAAF in SCS/Taiwan situation would escalate to nukes. At least, I don't think it's
likely. Definitely a nonzero chance, maybe a coin toss, but Taiwan isn't core territory for either Power.
Invasion, now . . well, there's the magic power that comes with having 'em. No one invades you, ever.
Also,outside factors could change the math here, like a megavolcano under the west antarctic ice sheet or something that raises ocean levels by meters. That redefines "back against the wall". If your country loses all access to fresh water, well, you might as well be under occupation or destroyed, so you might use your nukes aggressively. Just don't accidentally drop them in the water you're trying to get.
Invasion, now . . well, there's the magic power that comes with having 'em. No one invades you, ever.
Also,outside factors could change the math here, like a megavolcano under the west antarctic ice sheet or something that raises ocean levels by meters. That redefines "back against the wall". If your country loses all access to fresh water, well, you might as well be under occupation or destroyed, so you might use your nukes aggressively. Just don't accidentally drop them in the water you're trying to get.