Mutually assured destruction sounds nice in movies but in reality, it stopped the mighty japanese empire. Some look at nukes as a way to sacrifice millions to save billions. Some think even a nuke power like the US will not continue to escalate after a nuclear war because of political red tape or MAD,the US or Russia for examples might surrender and accept loss instead of riskiny a global nuclear war.
If China starts invading asia for example, the UN can be used to sanction or even coordinate a resistance effort both diplomatic and kinetic before it gets out of control.
Unless you are japanese that empire will not have treated you nicely. "The man in the high castle" shows how it might have been under japanese rule. No thanks.
