[XorNot]

Asking the wrong question: the nuclear bomb was developed before nuclear power, and was developed in an environment where it was suspected that the Germans and Japanese - which the US was at war with - were trying to do the same.

But there's another component to that too: the ability to "level another nation" isn't quite a function of nuclear weaponry - it's much more a function of rocketry which makes ICBMs possible. It's perhaps an interesting thought exercise that a world without nuclear weapons could still have a very large scale build up of say, ICBM-delivered thermobaric weapons which would enable a country to rain effective destruction down on any other while being at no risk of being responded to in-kind.

Nukes short-circuited that: because it's much cheaper to put a nuke on an ICBM, and as such all ICBMs are presumed to be nuclear until proven otherwise, as a result now, no one uses ICBM technology to deliver anything but nuclear weapons since launching anything else invites a nuclear response (one of the big problems with most of the "carrier-killed" missile concepts - their launch sites look indistinguishable from nuclear ICBMs).