Comment by Spooky23

Ukraine crossed the Russian frontier. The Russians escalated by importing cannon fodder from North Korea.

I think the better question would be if China crossed the Yalu River today and joined the North Koreans to assault South Korea, what would the response of the US, South Korea, and Japan be? The latter two can trivially develop nuclear weapons if the US security situation degrades.

I think wielding nuclear weapons requires a baseline level of competence to exploit.