"A Canticle for Leibowitz" by Walter Miller

The only novel published by Miller during his lifetime consists for three novellas previously published in SciFi magazines, but significantly modified to fit the novel form.  The three parts depict a post-apocaliptic world, after an all-out nuclear war has wiped most of humanity in the 1960s.  The first part happens around 2700s, the second part happens around 3100s, and the last part around 3800s when humans have developed space flight, extra-solar colonies, and (unfortunately) nuclear weapons again.  The idea promulgated is that the time between bronze age and nuclear age is around 3-4,000 years, and will always follow that pattern.

In the first part, about 6 centuries after a moronic nuclear war among moronic nations has devastated the Earth and killed off most of the humans.  The remaining humans called themselves "Simpletons' and started killing off all scientists by burning them alive, and when they killed all of them - they started killing anyone literate, moronism and illiteracy being haled up as the highest virtues among the human-animals populating the planet.  Only the Catholic order of Leibowitz has dedicated itself to preserving the remaining knowledge of the human race, be it scraps of written paper or half-burned page of a physics textbook.

Brother Francis from the wild wastes of Utah is doing his Lent fasting while discovering a fallout shelter with important artifacts inside while the canonization of the Blessed Leibowitz proceeds in the Abbey (within the borders of the Empire of Denver) and in New Rome (somewhere in West Virginia).  The roads between the few populated cities are populated by mutated half-humans half-animals who kill everything that moves for loot and food, and that befell brother Francis as well.

In the second part, another six centuries later, human civilization has achieved around medieval scientific development, the first electrical light experiment is successful and the primitive empires on the North American continent are vying for supremacy, most people still being illiterate; living in squalor and primitivism, both in social customs and in overall development.  The Abbey of St. Leibowitz is now a center of learning, having preserved many books from the last nuclear age of humanity, which are essential for re-discovery of science.

In the third part humanity has surpassed the current scientific age and has not only Solar but also colonies on other star systems (Miller mistakenly hoping that atomic drives would take us to the stars).  However the moronism of human politicians and their artificial creations called 'nations' - 'patriotism' 'us vs them' and similar money drivel causes another nuclear war that devastates the planet yet again, despite the politician snakes and reptillian disgustoids who run the society blaming  the 'other' side. Crazed monkeys be crazed monkeys.

I've read some complaints about the "Catholic-ness" of the novel online.  I guess there's a streak of Catholic-haters out there.  I am not Catholic, but have nothing against Catholicism and Miller has converted from Judaism to Catholicism, so it is only expected Catholic themes to have a prominent place in his work.  The theme of Catholicism is appropriate and justified in the book and not out of step with many historical parallels (after all, many of the great scientists of the past have been catholic monks and priests).