There is a tide in the affairs of men. It cycles with a period of about three hundred years. During its flood, farms and businesses prosper, and great empires enjoy golden ages. During its ebb, war and famine stalk the land, and states collapse into barbarism.

Chinese population over time

At least this is the thesis of Peter Turchin and Sergey Nefedov, authors of Secular Cycles. They start off Malthusian: due to natural reproduction, population will keep increasing until it reaches the limits of what the land can support. At that point, everyone will be stuck at subsistence level. If any group ever enjoys a standard of living above subsistence level, they will keep reproducing until they are back down at subsistence.

Standard Malthusian theory evokes images of a population stable at subsistence level forever. But Turchin and Nefedov argues this isn't how it works. A population at subsistence will always be one meal away from starving. When a famine hits, many of them will starve. When a plague hits, they will already be too sickly to fight it off. When conflict arrives, they will be desperate enough to enlist in the armies of whichever warlord can offer them a warm meal.

These are not piecemeal events, picking off just enough of the population to bring it back to subsistence. They are great cataclysms. The Black Plague killed 30% – 60% of Europeans; the Antonine Plague of Rome was almost as deadly. The Thirty Years War killed 25% – 40% of Germans; the Time of Troubles may have killed 50% of medieval Russia.

Thus the secular cycle. When population is low, everyone has more than enough land. People grow rich and reproduce. As time goes on, the same amount of farmland gets split among more and more people. Wages are driven down to subsistence. War, Famine, and Pestilence ravage the land, with Death not far behind. The killings continue until population is low again, at which point the cycle starts over.

This applies mostly to peasants, who are most at risk of starving. But nobles go through a related process. As a cycle begins, their numbers are low. As time goes on, their population expands, both through natural reproduction and through upward mobility. Eventually, there are more nobles than there are good positions…

(this part confused me a little. Shouldn't number of good positions scale with population? IE if one baron rules 1,000 peasants, the number of baronial positions should scale with the size of a society. I think T&N hint at a few answers. First, some positions are absolute rather than relative, eg "King" or "Minister of the Economy". Second, noble numbers may sometimes increase faster than peasant numbers, since nobles have more food and better chances to reproduce. Third, during boom times, the ranks of nobles are swelled through upward mobility. Fourth, conspicuous consumption is a ratchet effect: during boom times, the expectations of nobility should gradually rise. Fifth, sometimes the relevant denominator is not peasants but land: if a noble only has one acre of land, it doesn't matter how many peasants he controls. Sixth, nobles usually survive famines and plagues pretty well, so after those have done their work, there are far fewer peasants but basically the same number of nobles. All of these factors contribute to excess noble population – or as T&N call it, "elite overproduction")

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