Secular Cycles Theory
"When Turchin refined the concept of cliodynamics with two colleagues — Sergey Nefedov of the Institute of History and Archaeology in Yekaterinburg, Russia, and Andrey Korotayev of the Russian State University for the Humanities in Moscow — the researchers found that two trends dominate the data on political instability. The first, which they call the secular cycle, extends over two to three centuries. It starts with a relatively egalitarian society, in which supply and demand for labour roughly balance out. In time, the population grows, labour supply outstrips demand, elites form and the living standards of the poorest fall. At a certain point, the society becomes top-heavy with elites, who start fighting for power. Political instability ensues and leads to collapse, and the cycle begins again."
- Laura Spinney 
From the Wikipedia:
"Recently the most important contributions to the development of the mathematical models of long-term ("secular") sociodemographic cycles have been made by Sergey Nefedov, Peter Turchin, Andrey Korotayev, and Sergey Malkov. What is important is that on the basis of their models Nefedov, Turchin and Malkov have managed to demonstrate that sociodemographic cycles were a basic feature of complex agrarian systems (and not a specifically Chinese or European phenomenon).
The basic logic of these models is as follows:
- After the population reaches the ceiling of the carrying capacity of land, its growth rate declines toward near-zero values.
- The system experiences significant stress with decline in the living standards of the common population, increasing the severity of famines, growing rebellions etc.
- As has been shown by Nefedov, most complex agrarian systems had considerable reserves for stability, however, within 50–150 years these reserves were usually exhausted and the system experienced a demographic collapse (a Malthusian catastrophe), when increasingly severe famines, epidemics, increasing internal warfare and other disasters led to a considerable decline of population.
- As a result of this collapse, free resources became available, per capita production and consumption considerably increased, the population growth resumed and a new sociodemographic cycle started.
It has become possible to model these dynamics mathematically in a rather effective way. Note that the modern theories of political-demographic cycles do not deny the presence of trend dynamics and attempt at the study of the interaction between cyclical and trend components of historical dynamics.'
The models have two main phases, each with two subphases.
- Integrative phase
- Expansion (growth)
- Stagflation (compression)
- Disintegrative phase
- Crisis phase (state breakdown)
- Depression / intercycle
An intercycle is where a functioning state collapses and takes some time to rebuild.
Disintegrative phases typically do not have continuous disorder, but instead periods of strife alternating with relatively peaceful periods. This alternation typically has a period of about two human generation times (40 - 60 years), and Turchin calls it a "fathers and sons" cycle.