What is the setting of the novel, Alien Citadel?

Alien Citadel is set on the planet, Earth, but on a future Earth that only barely resembles our own world. In this future world, humans live in fear, hiding from the Slavers, the planet's new masters. The planet is covered by desert wasteland, forested wilderness, and radioactive firesands where monstrous mutant creatures prowl. There is nothing left of civilization and very little hope among the people who live there.