1980’s The Silver Sun is the second volume in Nancy Springer’s The Book of the Isle series. The Silver Sun is a heavily revised edition of 1977’s The Book of Suns.
The Isle was home to human folly but not willful malevolence. That changed when the Easterners attacked. Divided amongst themselves, the kingdoms of the Isle failed to unify against the existential threat posed by the invaders. Consequently, most of the Isle fell to the Easterners, whose rule is as deliberately cruel as it is unjust.
Seven generations after the invasion, hope appears in the form of a naked man running through a forest.