Fritz Leiber's classic novel Gather, Darkness! (1950.) This was serialized in Astounding from May through July, 1943. John W. Campbell fed this idea to more than one author: Robert Heinlein's The Day After Tomorrow is his version of the idea, and Campbell's own treatment is the novella "All."

There is a new dark age hundreds of years after the dawn of the Atomic Age, where the scientists, having lost faith in democracy, sieze control of the world in order to save it. They become a high-tech priesthood who maintain their power by setting up a false religion and performing miracles by scientific trickery. The Resistance to this uses super-science of their own disguised as Witchcraft. We follow the tale of Brother Jarles, a renegade priest of the Hierarchy. His ideals place him between the two sides, and he ends up pursued by both. Soon will come the Witches' Revolt, when he will end up playing a pivotal role.