the stories in the book are set on two planets in a distant solar system, werel and yeowe, inhabited by humans placed there by the ancient hainish. (this 'werel' is not the same as the world called werel in le guin's "planet of exile" and "city of illusions".) werel has a long history of institutional enslavement of its lighter-skinned ethnic groups by its darker-skinned ethnic groups (the latter's derogatory term for the former is "dusties"). when the ekumen recontacted the werelians, the shock spurred one of the werelian nations, voe deo, to develop a space program and settle the other inhabitable planet in the system, yeowe, transporting a primarily slave population to do so. eventually the slaves on yeowe conducted a successful revolt and gained their independence, an event that occurred in the fairly recent past of the four stories. the nations of werel are nervous that the "assets" on that planet might attempt the same thing for themselves.