The visitor - Sheri S. Tepper

Sheri Tepper, one of the foremost science fiction writers in the world, gives us an exciting, evocative and thought-provoking tale where science and magic meet head-on. A group of colonists, waking every few hundred years to see what's been happening on the planet they fled to from a dying Earth, watch as the systems and rules they set in place so long ago become
debased and decayed. The corrupt leaders govern by oppression, but technological resources run low and the knowledge of how to replace them is lost in the mists of time. Instead, the power-hungry leaders turn to sorcery of the blackest kind, kindled by pain and despair. And when they
launch a religious crusade to wipe out all those who won't conform to the government's ever-more-stringent dictates, not even the original colonists - the new gods - are safe from the ravaging sorcery-fuelled armies of the righteous . . .