Gibbon begat Spengler, who begat Toynbee, who begat Hari Seldon - or so it seemed to me in high school. Arnold Toynbee has pretty much fallen down the memory hole, but in the mid-20th century his reputation was considerable. I'm sure I learned his name from Clarke, who mentions him fairly often, in one story even naming a spaceship Arnold Toynbee. Oddly, Clarke never much worked the future-history street corner. I don't know if Asimov ever mentions Toynbee, but A Study of History is the perfect companion piece for the Foundation Trilogy.*
Like Spengler, Toynbee was big on the grand cycles of history, the rise and fall of civilizations. Unlike Spingler, however, Toynbee does not fall back on semi-mystical mumbo jumbo about civilizations being organic entities with a fixed lifespan. (Later he fell back on a different semi-mystical mumbo jumbo.) Although most past civilizations have declined and fallen, this is not inevitable; a flexible enough society might keep winning the game of Civilization indefinitely.
You win, says Toynbee, by growing through a cycle of challenge and response. Challenge usually means something like "Vikings show up," to which the response may be organizing the fyrd, or simply giving them Normandy provided that they ask for it in French. Each response, if successful, usually ends up planting the germ of the next challenge. The Vikings learn French and become Normans, for which the response is to ship them off to conquer England and Sicily.
Or, suppose an academic enclave on the fringes of a declining empire faces the challenge of petty kingdoms that have broken away from imperial control. It responds by repackaging its learning as religious magic to awe the natives. This works, but the religious establishment gets out of hand, only to be muscled aside by trading interests ... each Seldon Crisis leading logically to the next.
If a civilization fails to handle a Seldon Crisis it "breaks down," and spends the rest of its history - some 800-1100 years, depending on how you measure - trying and failing to patch things up. The civilization first enters into a Time of Troubles, persisting and destructive internal warfare, that last about 400 years. The Time of Troubles ends with the last guy standing, who founds a Universal State that will in turn last about 400 years.
Toynbee's prototype for this grand cycle is classical civilization. The Greeks were going along fine, he says, till the Pelopponesian War (431-404 BC) screwed it all up for them. The Time of Troubles, with Greek and then semi-Greek states bashing endlessly and pointlessly away at each other, lasts a nice exact 400 years till the Battle of Actium in 31 BC, after which Cleopatra 's asp leaves Augustus the last guy standing. Another 409 years - close enough! - takes you to the Battle of Adrianople in AD 378, when the Goths wiped out a full Roman army, for Toynbee the effective end of the Empire. (Apparently Theodosius the Great doesn't count, let alone Justinian.)
After the fall comes a 300-year fallow period, an interregnum, at the end of which one or more new civilizations will rise out of the ashes of the old one to embark on their own Seldonian adventures. Just 309 years from Adrianople takes you to the battle of Tertry in 687 - not exactly household-name stuff, but the winner was a guy named Pepin of Heristal, majordomo to a Merovingian king whose name no one then or since has bothered with (Theuderic III). Majordomo sounds cooler when you translate it as Mayor of the Palace. Pepin's son was Charles Martel, the Hammer, his grandson was Charlemagne, and we are off to the races with the Rise of the West.
It turns out that nearly all other fallen civilizations have followed this same trajectory on the way down - admittedly Toynbee was not above a little hammering to help things fit. Within the 400-year primary wavelength he identifies a 200-year harmonic - federal ideas were in vogue for a while in post-Alexandrine Greece, to Toynbee a "rally" amid the Time of Troubles, while the Roman rough patch between Marcus Antonius and Diocletian is a "rout" foreshadowing the eventual fall. Even Justinian can be seen as a final "rally," even though Rome had already fallen. Toynbee notes some multi-generation social rhythms that are fairly well-established, such as the cultural naturalization of immigrant populations, to suggest that these long cycles have some natural basis.
All of this is enormously persuasive when you are a geeky teenager, and Toynbee seemed like the Newton or Darwin of history. I was actually motivated to do some critical research - and learned to my dismay that professional historians regarded it all as sophisticated BS. The rap on him, in a nutshell, is that he did a lot of hammering to make other civilizations fit the schedule, in fact beating world history pretty much out of recognition.
Still, Toynbee's scheme is inherently cool, and it just asks to be used as a framework for a future history. Bound up in this is the interesting little question of what his model says about the West. Are we still growing, successfully handling each Seldon Crisis as it comes along, or did we already "break down" at some point in the past? More on that next time!
* Foundation, Foundation and Empire, and Second Foundation, all published as books in the early 1950s. Accept no substitutes! Asimov's other much later "Foundation" books are generally lame, and don't count.