Russia would never threaten China with nukes, because 1) China ALSO has nukes, and 2) China has been the only thing keeping Russia afloat recently.

But it would have to be a scorched earth kind of invasion. The kind that pisses off basically everyone, because it leaves every single Russian, military, or citizen, dead. They’d have to come in, take everything, and kill everything. Take the land.

First of all, if you’re being invaded by an army planning to genocide your entire population, then you have no reason not to use every weapon in your arsenal. If the options are A: China kills 100% of your populace or B: Launch nukes and even 1% of your populace survives whatever follows, then B is the most rational choice.

Secondly, there’s no reason to assume that states will make rational decisions to begin with. I’d say the current state of affairs in Ukraine is a very good example of that in action. So even if China wasn’t planning to genocide all of Russia, even if it was some kind of “benevolent” invasion where they were going to tiptoe around the flower beds, gently pry Putin out of the Kremlin, and basically leave everything the same except that now Russians pay for groceries with renminbi instead of rubles… there’s still every reason to imagine that Putin and his top brass would still launch nukes on the mere principle of the thing.

So no, let’s not glibly plan for a fast forward on nuclear Armageddon, thank you very much.