Post-apocalyptic, after the bomb, when the radiation's died down. The world's a wasteland but is slowly making a come back. Most of human society is tribal, with major cities that managed to make it thought not overly damaged are becoming major centers of comerce where you can get most anything you like. There are of course roaving bands of badies and such.
I was thinking of starting in one of the tribes and being forced to leave because of a catastrophy (ie. slavers come through and gather up the village, roaving monsters devour everyone, etc.)