The other word you are looking for is nuclear
BTW if they threaten Japan than the only thing that will happen is more threats and idle rhetoric from the UN. Even if NK does nuke somebody, I still doubt any other country would break thiers out, unless it was Israel (who is widely believed to have nukes but is not confirmed) Nukes going off in the open atmosphere cause global problems. I hardly think the US wants a nice fat cloud of radioactive fallout to cruise over Japan and then continue on to the west coast. I think large scale carpet bombing would be the retribution, and it wouldn't be just us doing it, we would probably make China do it since NK is thier goddam toy. All of that is my opinion based on no facts whatsoever, just my impression on what would happen.