After the war, little was left of the world. Most major population centers had been wiped out by missile attacks, and many areas became uninhabitable due to radioactive fallout - not to mention the innumerable demons which had appeared.
Humanity moved to new homes: underground cities, safe from the radiation and demons grew, as well as a few above-ground settlements in areas with lower concentrations of the two hostile factors existed.

The areas in-between these places came to be known as The Endless Wasteland