This builds on model based research described in in 2013 PNAS paper which is open access that I read and discussed, either at this blog or in comments elsewhere at the time. The abstract of the paper reads as follows:
How did human societies evolve from small groups, integrated by face-to-face cooperation, to huge anonymous societies of today, typically organized as states? Why is there so much variation in the ability of different human populations to construct viable states?
Existing theories are usually formulated as verbal models and, as a result, do not yield sharply defined, quantitative predictions that could be unambiguously tested with data.
Here we develop a cultural evolutionary model that predicts where and when the largest-scale complex societies arose in human history. The central premise of the model, which we test, is that costly institutions that enabled large human groups to function without splitting up evolved as a result of intense competition between societies—primarily warfare. Warfare intensity, in turn, depended on the spread of historically attested military technologies (e.g., chariots and cavalry) and on geographic factors (e.g., rugged landscape).
The model was simulated within a realistic landscape of the Afroeurasian landmass and its predictions were tested against a large dataset documenting the spatiotemporal distribution of historical large-scale societies in Afroeurasia between 1,500 BCE and 1,500 CE. The model-predicted pattern of spread of large-scale societies was very similar to the observed one. Overall, the model explained 65% of variance in the data. An alternative model, omitting the effect of diffusing military technologies, explained only 16% of variance.
Our results support theories that emphasize the role of institutions in state-building and suggest a possible explanation why a long history of statehood is positively correlated with political stability, institutional quality, and income per capita.I'm generally pretty skeptical of model based research of this kind, but Turchin's stochastic model is one of the best examples of the type, doing an excellent job of striking a balance between having too many and too few parameters, and of modeling them in a way that reproduces alternative histories that are similar in broad outlines to historical reality. The fact that the model can do so strongly suggests that the parameters that the model considers are basically the right ones.
If I recall correctly, the guts of the model as applied also exploit a recurring motif in forest level views of history - conflict between "barbarian" herder societies (often in mountains or dry steppes) that tend to prevail in "bad times" and "civilized" farmer societies that tend to prevail when conditions are more optimal.
The other question, of course, is whether we as a species have outgrown this kind of dynamic, or if it continues to drive our cultural evolution on more or less the same basis that it did from the late Bronze Age through the Middle Ages.