After The Fall: EarthFall
After-Earth is a poisoned land.
Even without the hundreds of bombs dropped by the dying governments, the chemical weapons unleashed by the terrorist organizations as they fought weakly to keep themselves relevant, the world would have still died. As the cities crumbled the offal of man ruined the land, the chemicals that made their buildings burnt and floated into the air coating the world in ash that took 100 years to deteriorate. Now fresh water is scarce, what people collect they gain from catchments, what water flows in the ground is almost certainly poisoned.
The world attempts to throw off those it used to nourish.
The Little Desert and the Earth-Sun are both baked clay and sand deserts offering little in the way of life. Yet they shelter those who would live their from the radiation still trapped in the mountains.
Villages and towns, crop up around small bits of fresh water, that sometimes spoils. Until that time towns circle the water holes.