On a related note, Cliodynamics.
Not Psychohistory, Cliodynamics
And from the pdf:
agrarian societies experience periods of instability about a century long every two or three centuries.
Applying the above approach to eight secular cycles in medieval and early modern England, France, the Roman Empire and Russia, we find that the number of instability events per decade is always several times higher when the population was declining than when it was increasing. The probability of this happening by chance is vanishingly small. The same pattern holds for the eight dynasties that unified China, from the Western Han to the Qing, and for Egypt from the Hellenistic to the Ottoman periods.
fundamental principles. Population growth beyond the means of subsistence leads to declining levels of consumption and popular discontent, but this is not enough to destabilize agrarian societies. Peasant uprisings have little chance of success when the governing élites are unified and the state is strong.
The connection between population dynamics and instability is indirect, mediated by the long-term effects of population growth on social structures. One effect is the increasing number of aspirants for élite positions, resulting in rivalry and factionalism. Another consequence is persistent inflation, which causes a decline in real revenues and a developing fiscal crisis of the state. As these trends intensify, they result in state bankruptcy and a loss of military control; conflict among élite factions; and a combination of élite-mobilized and popular uprisings, leading to the breakdown of central authority.
theories developed and tested on preindustrial data must be modified before they can be applied to contemporary social dynamics. Happily, there are indications that our theories will not need to be replaced wholesale. Rapid demographic change and élite overproduction were still important factors in twentieth-century revolutions.
Like other systems with nonlinear feedback, societies often respond to interventions in surprising ways. When the Assembly of Notables refused to approve a new land tax in 1787, they did not intend to start the French Revolution, in which many of them lost their heads. When Tony Blair was Britain's prime minister, he set out to increase the proportion of youth getting higher education to 50%. He was presumably unaware that the overabundance of young people with advanced education preceded the political crises of the age of revolutions in Western Europe, in late Tokugawa Japan and in modern Iran and the Soviet Union.
