They were used. Twice. Then we as a human collective agreed that they are too dangerous to ever be used again. The only reason they're still around is because of scare mongering. "but the baddies have them, so we have to have them too!"
Nuclear war isn't an option, it will end civilization. No one will launch, and if for some reason someone does, WW3 is started, and over in 2 hours, with every nuclear capable country dead, and probably some other countries as casualties.