Who or what caused the Change in SM Stirling's Emberverse series? Was it Satan? See comments here. I understood that it was the good guys/gods. See here, including the Addendum dated today, and here. This view is backed up by the Wikipedia article on the novel (see here), which states that humanity had to be deprived of high technology so that it would have time to mature without destroying itself first. I will return to this issue when I have more information to hand.