Ages of Discord -- American History's Big Cycle -- by Peter Turchin
Peter Turchin: US-History Cycles
Peter Turchin and others had previously done work on history cyclicity in preindustrial societies, finding lots of evidence of cycles over the centuries. These cycles, they conclude, are driven by structural and demographic factors.
The cycles have integrative and disintegrative phases, rising and falling ones. Each phase is self-limiting, and turns into the other phase. Each cycle lasts roughly 300 - 400 years.
The integrative phase starts with both commoners and elites having relatively small populations, and there is plenty of agricultural production to go around. Commoners grow until they start to run out of arable land, and elites also grow -- and grow faster. This drives down the standard of living of the commoners and leads into the disintegrative phase.
In the disintegrative phase, elites fight each other over top positions, because such positions do not multiply along with the elites. They do so until enough of them are either killed or exiled or demoted. The commoner population also declines from the fighting, and sometimes also from plagues, and when the fighting dies down, an integrative phase may start.
Civil wars are usually not continuous but episodic, following a two-generation or fathers-and-sons cycle. One generation fights, and then its successor generation does not wish the relive the experience and does not fight. For the successor's successor, the original strife is not something that they directly experienced, so they feel less inhibited about fighting.
In an integrative phase, a nation may gain territory, while in a disintegrative phase, a nation may lose territory -- sometimes all of it, thus being conquered.
It seems to fit ancient Rome, medieval and early modern Britain, France, and Russia, and Imperial China. But does it fit industrialized societies?