The world was scorched for over a hundred years during the war with the aliens and finally they left. Unfortunately not much of humanity survived. Most did so by scattering to groups so small they werent noticed or moving into caves or remote islands. Those who chose to remain where they were died or survived through very hard times. It came as a shock when the aliens left and women became a source of money, to be used and sold by the wanderers to the tribes. After a hundred years human nature has taken over once more.