JetStream
Chieftain
The Atom Bomb may finish a city, but that is not a game finisher in itself at all. Even if it's a capital, it will only mean a shift to another city. Also, it will only affect 1 civ. I've even won after being nuked.
That's why i say in a sense since if you stock pile and release these consistently by building or rush buying then you can pretty much wipe everyone out except their capitals.
also my second paragraph is my opinion that should be done, in case they want it to become a Victory Condition which obviously finishes the game.