Messing things up even after the end
The Long Tomorrow, by Leigh Brackett (1955; **** of 5)
A Gift Upon the Shore, by M.K. Wren (1990; **** of 5)
A Canticle for Leibowitz, by Walter M. Miller, Jr. (1959; ***1/2 of 5)
Swan Song, by Robert R. McCammon (1987; *** of 5)
The Stand, by Stephen King (1990; ** of 5)
Religion plays a major, even inordinate, role in many conceptions of what life might be like after civilization collapses. That, of course, surprises no one. One factor in why armageddon in any form is a threat is that fundamentalist dogma says it basically has to happen for their doctrine to be fulfilled. To prove their way is the only "right" way, they promote massive destruction, although not always actively.
McCammon's Swan Song is probably the most obvious example of this I've ever read, possibly exceeded only by Stephen King's The Stand. Both of these lengthy tomes have strongly dualistic themes, with rampaging inhuman evil leading human evil in an effort to kill off the last of human hope. King's version is overtly Christian in tone, even to the point of having the evil forces based in Las Vegas, while McCammon's has almost a pagan feel, with its focus on a girl who can grow plants magically, an obvious mother goddess image. The main evil character in both is almost identical, right down to his ability to shapeshift, making me wonder if one inspired the other.
An interesting element of Swan Song, though, is a key good character's blatant rejection of the fundamentalist insanity -- literally. Sister, a former NYC street person, starts off being incredibly delusional, ranting to everyone passing by that "the Rapture" would be a wonderful thing. Appropriately enough, she calls herself Sister Creep at that time. Although she never remembers her real name, after the bombs fall, she does remember what happened to her to cause her madness and realizes the whole concept of "Rapture" is crap. Despite the existence of evil, nobody's coming down to swoop the good guys into a wonderful other world -- the only wonderful world that'll exist is if good people create it themselves.
That latter theme is sort of echoed in both Wren and Brackett, but in a different way. In both, a small element of society is trying to save the science and printed wisdom of our civilization ... to the great horror and religious opposition of the majority. Wren's tale is a microcosm of Brackett's -- it focuses on just one group of people, with two who want to save books and teach the children to think opposing several who believe all books are evil except the Holy Babble. The fact that the two skeptics are women in a very patriarchal cult and possibly lesbian lovers (that's never clearly stated, but definitely suggested) creates an extra level of tension.
In Brackett, the fundamentalist impulse reigns supreme, in the form of New Mennonites who overtly reject the science and cities of 20th Century America. The book has a good point that a back-to-simplicity mindset would indeed be a survival trait in the decades after WW3, but coupling that with venomous, Babble-quoting lynchings of people even suspected of harboring scientific devices or ideas is not. They go so far as to pass a 30th Amendment to the US Constitution banning all communities of over 1,000 people or 200 buildings. (Brackett writes one of the few post-WW3 books that postulates a new dark age in which the US survives as a country; in this case, our society is dropped back into the 18th or 19th Century.)
Brackett's New Mennonites would fit right into the Simplification envisioned by Miller: rampaging mobs of self-described "simpletons" murder the vast majority of educated people, then even literate folks, and burn any books they can in their anger at the folks they blame for WW3. That Simplification, however, doesn't specifically have a religious motive; in fact, the whole point of the book is that the Catholic church helps save what knowledge it can.
The irony there, however, is subtle -- the key character spurring the creation of the monastic order of "bookleggers and memorizers" is a scientific, secular Jew (the title character) later canonized for alleged miracles having nothing to do with his eforts to save knowledge. Furthermore, although the monks don't hide the material they slavishly copy over the centuries, they don't actively share or utilize it either. In 3074, the monks have had the printing press for a century ... largely becasue an abbot 500 years earlier specifically rejected a proposal to build one as unnecessary because there was no market for cheap books. (Never mind the fact that cheap books would have made it possible to educate people more easily; in 3074, there's a line noting that the village of Sanly Bowitts has the "fantastic literary rate of eight percent" despite being just a few miles from the abbey and its 100% literacy rate.)
That kind of dogmatic foot-dragging is common in Miller's chronicle. In fact, I'd say organized religion's strength (when not being used to promote hostility) is it's ability to preserve the past when the average level of society is low, but it is largely ineffectual at dealing with the present or promoting a healthy future when average people are educated. The browbeating that works on the ignorant only annoys and turns off the educated, but many churches cannot adapt effectively to cultural change, and tend to speak with a voice of unreason cloaked as "morality."
Toward the end, we see references to the Pope praying for peace as another nuclear war threatens a re-established global civilization that has progressed beyond ours technologically (including space colonies) ... but doing nothing to actually prevent war. Instead of criticizing people for their behavior, how about promoting the common ground humans share regardless of nationality? Had the Church done THAT over the centuries, there probably wouldn't be a threat of global war (Miller's future war OR modern war).