The Change series by S M Stirling - The Emberverse series

The Emberverse series, or the Change World, is set of alternate history, post-apocalyptic novels written by S. M. Stirling. The novels focus on the events after "The Change", which caused electricity, guns, explosives, internal combustion engines and steam power to stop working. Most of the action in the series takes place in the Willamette Valley of the U.S. state of Oregon. The primary focus of the first three books of the series is how people survive the loss of 500 years of technological progress. Meanwhile, a conflict escalates between the Portland-based neo-feudal dictatorship created by a sociopathic former history professor, and the free communities of the Willamette Valley. The most notable are the Wiccan Clan Mackenzie and a group led by a former Marine, called the Bearkillers.