Nuclear deterrence is basically "whoever nukes first gets nuked second". As long as retaliation is assured, no country (barred extremists) will start a nuclear

Nuclear deterrence is basically "whoever nukes first gets nuked second". As long as retaliation is assured, no country (barred extremists) will start a nuclear war unless someone else fired at them first. Nuclear weapons will only be used against non-nuclear countries. Reagan wanted to upset that balance with his failed "Star Wars" program, but seeing how the nuclear powers interact, it seems no one has achieved asymmetrical nuking. Yet.