Let me just list an example or fifteen:
- WHEN WORLDS COLLIDE. The central image, the shock-value, of that movie (and the book that inspired it) is the image of cosmic destruction, the downfall of civilization. You might think I would see a parallel between the Apocalypse of St. John and the destruction of the Earth, but no: the new world to which the Space Ark flies is not the new heaven and the new earth of St. John. The people aboard are more like the manuscripts monks tirelessly copied in their (mostly successful) attempt to keep alive the ghost of the ancient world. Speaking of which:
- A CANTICLE FOR LEIBOWITZ by Miller. Routinely on best-SF-of-all-time lists, it is little more than a futurization (if I may coin that awkward term) of the Fall of the Empire and the role of the Dark Ages Church as a preserver of knowledge.
- FOUNDATION by Asimov. Gibbon's Decline and Fall in SPAAAAACE!
- ROAD WARRIOR. Or list any book or movie about the New Dark Ages. (I list Mel Gibson's contribution to post-Fall fiction because it is a favorite of mine.)
- TO CRUSH THE MOON by Wil McCarthy. This is an incredible tour-de-force of a fall from a posthuman, atomic-engineering-level supercivilization. It deserves more publicity. Go out and read it, please.
- SHADOW OF THE TORTURER by Gene Wolfe. Has some of the look and feel of Middle-Ages Byzantium, mingled with a Vancean "DYING EARTH" flavor.
- FARNHAM'S FREEHOLD by Heinlein. Paynim bad guys take over after American civilization falls.
- DUNE. Paynim good guys take over after Imperial civilization falls. This is the fall of Byzantium (complete with Byzantine intrigue) to the forces from the desert, motivated by a new religion.
- LEST DARKNESS FALL by de Camp . Time traveler tries to halt the fall of Roman civilization through double-entry bookkeeping.
- WIZARD OF LINN by A.E. van Vogt. "I , Caludius" in SPAAAAACE!
- THE TIME MACHINE by H.G. Wells. The far future holds, not utopia, but a mankind forced by evolution into helpless Eloi and maneating Morlocks.
- THINGS TO COME by H.G. Wells. After the Dark Ages, we will all dress like Romans in togas, and shoot our married astronaut couple to the moon in a giant space gun.
- SIXTH COLUMN, CONNECTICUT YANKEE IN KING ARTHUR'S COURT, AGAINST THE FALL OF NIGHT, BUCK ROGERS, THUNDARR THE BARBARIAN etc. etc.
Why is the Decline and Fall of civilization is a central theme that crops up again and again in Science Fiction?
My guess: Science Fiction deals, among other themes, with the role of technology in shaping society. A civilization toppling into a dark age, loosing its technology, or climbing out of a dark age, regaining its technology, is an adroit setting in which to explore the interconnectedness of social and legal (and personal) factors and the level of technology a society can maintain. Technology becomes more precious when it is about to slip away.
The whole point of science fiction is that things change and history is without mercy. Science Fiction is all about the disorientation the reader fells when he realized Things to Come are not to be as Things Are Now. We look back at the Romans and we hope that It Can't Happen Now. People whose history retains no memory of such a huge shock and setback, a collapse and rebirth of civilization, might tend to think their societies are immortal, that the Son of Heaven will always be on the throne of the Forbidden City.