I got through Peter Turchin’s book End Times. It is definitely an interesting book. To summarize, organized human societies tend to develop a “wealth pump” whereby the wealthy and powerful influence the rules of the game to appropriate an ever larger share of a society’s wealth and power for themselves, at the expense of ordinary people. “Ordinary people” is not just the median or what we think of as the “middle class”, it is the bottom 90% of the wealth and income distribution. He shows hard evidence that the policies enacted in the U.S. represent the preferences of the top 10%. Not only are the preferences of the median citizen under-represented, they have NO statistical bearing on what is actually enacted. This situation tends to eventually reach a point of instability unless intentional and effective steps are taken to “shut down the wealth pump”, which happens occasionally. Instability can sometimes look like outright collapse into chaos, but it can also look like fracturing or breakup of a society into smaller entities, as happened with the “fall” of the Roman empire.
What makes the book a little different than other “cyclical theories of history” is first that he backs it up with statistical evidence gathered from many societies over a long period of time. Second, it is not the “immiseration” of the common people that leads to instability, but actually the growth of the “elites” due to the wealth pump. At some point, there are more elites that want to be in power than available positions of power. They fight amongst themselves, and their rhetoric may allow them to gain a following among the masses, but their preferences and interests still represent the rich and powerful class of which they are a part, and switching from one elite faction to another will not shut down the wealth pump.