Re: Sci-Fi help for my Fantisy world please
Um, for one, massive nuclear strikes would mean that the planet, for humans, would be uninhabitable for centuries, and I doubt very many species of animals would be able to survive either. There would be years of nuclear winter, radiation levels would be at unsafe levels, and it actually takes a while for nature to reclaim abandoned ruins. If you want to see a live example of nuclear damage and the effects of human abandonment, check things out about Chernobyl.
There are easier ways to severely deplete or even cleanse the human population of Earth without going through the consequences of worldwide nuclear warfare. There's pestilence, or just sheer abandonment as humans explore other areas of the universe.