China has had nukes for decades. I'm surprised they haven't increased their number to be like Russia so they can do a retalitory strike. Instead they are stuck at the tactical level they don't even have 1000 nukes. That's not a strategic threat they don't have enough nukes to wipe out humanity like we do or the Russians like how they could wipe us out if they launched them all.
We don't have enough nukes to depopulate the Earth. Even at the height of the Cold War, both alliances going all-out was questionable in whether or not it could have resulted in such, though it certainly would have killed billions between direct and indirect effects.
It's strategic enough. Their retaliatory strike wouldn't end us as a nation but it's plenty able to work as a deterrent. Plus, they're probably thinking in terms of great powers instead of the cold war superalliances—there's no bonus achieved for being able to target every major city in the western hemisphere with a separate rocket.
Ending us as a nation is a pretty tall order.
A brief search online shows that the Chinese are estimated to have somewhere around fifty ICBMs. That's missiles capable of actually hitting the Mainland USA, though some shorter-ranged ones can probably hit parts of Alaska.
The USA has a multi-layered ballistic missile shield system in place. Its exact capabilities are of course classified, and estimates to how effective it is are all over the place, but I've seen between 25-75% for each layer. If we take the pessimistic estimate, and assume all Chinese ICBMs launch successfully, that still ends up with ~23 getting through a 3-layered defensive shield.
23 nukes striking the US, likely almost entirely along the West coast, with some possibly targeting New York or DC (maybe one for the Panama Canal), the nation would be wounded, but
far from finished. Internal turmoil and fallout
might cause the nation to collapse, but it's
far from a certainty.
Now, if we go with optimistic estimates for interception (75%), which I think are
completely unrealistically optimistic at this stage of development, you end up with 2-3 nukes getting through, and that's not
remotely close enough to take the USA out. It's just enough to piss the US off and spur the kind of rise in national unity that 9/11 briefly did, but most likely with
much more enduring effects.
After either scenario, in return, China would functionally cease to exist as a nation, because the US nuclear arsenal was designed to be able to strike Russia more or less in its entirety, and China is just as easy to hit. If China is hit, it's not a question of 'will it be able to hold together,' it's a matter of there won't be enough of the Chinese military and economic infrastructure for it to be
possible for them to hold together.
Now, all of this doesn't change the fact that nuclear war
would be absolutely horrific and we want no part of that. This is the operational paradigm the CCP's leadership needs to keep in mind though, when they decide whether or not to push the button. If the US pushes the button in return, China loses, full stop, and as a result, the only reason they'll decide to play that game, is if they decide the US lacks the guts to push the button in return.