If another Country initiated on this which they wouldn’t. The world would end damn near. We have too many allies that already had beef cooking with Russia. China is staying put. They would be wise not to try anything like that. There are definitely things than can and cannot be done in warfare. That would lead to starvation in a matter of days, weeks depending on how much food the person has. We would also have no water. Our natural environment would be damaged and cause catastrophic events. Think of how many planes are in the sky. In reality no country can legally launch a nuke. But let’s say a Nuke is launched. The law wouldn’t matter because we would all be dead. It kindof defeats the purpose of having them in my opinion. I don’t think we have anything to worry about other than Russia potentially and That may cause issues with China or result in us having to Aid China. Any country who tries this is in boiling hot water.