Different groups have different degrees of cooperation .. cohesiveness and solidarity. .. Groups with high [cohesion] arise on .. frontier .. area where an imperial boundary coincides with a fault line between two [ethnic] communities .. places where between group competition is very intense. .. Only groups possessing high levels of [cohesion] can construct large empires. ..This sort of thinking is so unpopular among historians that only a non-historian like Turchin (a biologist) will write books like this today. I don't really know what to make of stuff like this. It is certainly true that empires rise and fall. It seems to me that there are, or were, things that happen to aging empires that made them vulnerable. But to think that the history of China since 200 BCE has been more or less than same as the history of Europe strikes me as silly. Charlemagne's empire was nothing like the Roman empire, and after that Europe saw no others. The Roman Empire held onto Greece and Asia Minor for more than a thousand years – we call them Byzantine, but they called themselves Romans – which makes mockery of all those inevitable fall theories.
Stability and internal peace bring prosperity, and prosperity causes population increase .. leads to overpopulation, .. causes lower wages, higher land rents, and falling per capital incomes. At first, low wages and high rents bring unparalleled wealth to the upper class, but as their numbers and appetites grow, they also begin to suffer from falling incomes. Declining standards of life breed discontent and strife. The elites turn to the state for employment and additional income and drive up its expenditures at the same time that the tax revenue declines. .. When the state’s finances collapse, it loses the control of the army and police. Freed from all restraints, strife among the elites escalates into civili war, while the discontent among the poor explodes into popular rebellions.
The collapse of order brings .. famine, war, pestilence, and death. .. Population declines and wages increase, while rents decline. .. Fortunes of the upper classes hit bottom. .. Civil wars thin the ranks of the elites. .. Intra-elite competition subsides, allowing the restoration of order. Stability and internal peace bring prosperity, and another cycle begins.
So maybe there are patterns. But there is also variation. And to compare, as Turchin likes to, ancient and medieval empires with modern hegemonic states strikes me as silly.