To Peter Turchin, who studies population dynamics at the University of Connecticut in Storrs, the appearance of three peaks of political instability at roughly 50-year intervals is not a coincidence. For the past 15 years, Turchin has been taking the mathematical techniques that once allowed him to track predator–prey cycles in forest ecosystems, and applying them to human history. He has analysed historical records on economic activity, demographic trends and outbursts of violence in the United States, and has come to the conclusion that a new wave of internal strife is already on its way1. The peak should occur in about 2020, he says, and will probably be at least as high as the one in around 1970. “I hope it won't be as bad as 1870,” he adds.

Turchin's approach — which he calls cliodynamics after Clio, the ancient Greek muse of history — is part of a groundswell of efforts to apply scientific methods to history by identifying and modelling the broad social forces that Turchin and his colleagues say shape all human societies. It is an attempt to show that “history is not 'just one damn thing after another'”, says Turchin, paraphrasing a saying often attributed to the late British historian Arnold Toynbee. 

Cliodynamics is viewed with deep scepticism by most academic historians, who tend to see history as a complex stew of chance, individual foibles and one-of-a-kind situations that no broad-brush 'science of history' will ever capture. “After a century of grand theory, from Marxism and social Darwinism to structuralism and postmodernism, most historians have abandoned the belief in general laws,” said Robert Darnton, a cultural historian at Harvard University in Cambridge, Massachusetts, in a column written in 1999.

Most think that phenomena such as political instability should be understood by constructing detailed narratives of what actually happened — always looking for patterns and regularities, but never forgetting that each outbreak emerged from a particular time and place. “We're doing what can be done, as opposed to aspiring after what can't,” says Daniel Szechi, who studies early-modern history at the University of Manchester, UK. “We're just too ignorant” to identify meaningful cycles, he adds.

But Turchin and his allies contend that the time is ripe to revisit general laws, thanks to tools such as nonlinear mathematics, simulations that can model the interactions of thousands or millions of individuals at once, and informatics technologies for gathering and analysing huge databases of historical information. And for some academics, at least, cliodynamics can't come a moment too soon. “Historians need to abandon the habit of thinking that it's enough to informally point to a sample of cases and to claim that observations generalize,” says Joseph Bulbulia, who studies the evolution of religion at Victoria University of Wellington in New Zealand.

From ecology to history

Turchin conceived cliodynamics during what he jokingly calls a midlife crisis: it was 1997, he was 40 years old, and he had come to feel that all the major ecological questions about population dynamics had been answered. History seemed to be the next frontier — perhaps because his father, the Russian computer scientist Valentin Turchin, had also wondered about the existence of general laws governing societies. (The elder Turchin's dissident writings about the origins of totalitarianism were among the reasons that the Soviet Union exiled him in 1977, after which he moved his family to the United States.)

What is new about cliodynamics isn't the search for patterns, Turchin explains. Historians have done valuable work correlating phenomena such as political instability with political, economic and demographic variables. What is different is the scale — Turchin and his colleagues are systematically collecting historical data that span centuries or even millennia — and the mathematical analysis of how the variables interact.

Periods of rioting and upheaval have recurred roughly every 50 years in US history.

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In their analysis of long-term social trends, advocates of cliodynamics focus on four main variables: population numbers, social structure, state strength and political instability. Each variable is measured in several ways. Social structure, for example, relies on factors such as health inequality — measured using proxies including quantitative data on life expectancies — and wealth inequality, measured by the ratio of the largest fortune to the median wage. Choosing appropriate proxies can be a challenge, because relevant data are often hard to find. No proxy is perfect, the researchers concede. But they try to minimize the problem by choosing at least two proxies for each variable.

Then, drawing on all the sources they can find — historical databases, newspaper archives, ethnographic studies — Turchin and his colleagues plot these proxies over time and look for trends, hoping to identify historical patterns and markers of future events. For example, it seems that indicators of corruption increase and political cooperation unravels when a period of instability or violence is imminent. Such analysis also allows the researchers to track the order in which the changes occur, so that they can tease out useful correlations that might lead to cause–effect explanations.

Endless cycles

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.

Superimposed on that secular trend, the researchers observe a shorter cycle that spans 50 years — roughly two generations. Turchin calls this the fathers-and-sons cycle: the father responds violently to a perceived social injustice; the son lives with the miserable legacy of the resulting conflict and abstains; the third generation begins again. Turchin likens this cycle to a forest fire that ignites and burns out, until a sufficient amount of underbrush accumulates and the cycle recommences.

These two interacting cycles, he says, fit patterns of instability across Europe and Asia from the fifth century BC onwards. Together, they describe the bumpy transition of the Roman Republic to the Roman Empire in the first century BC. He sees the same patterns in ancient Egypt, China and Russia, and says that they explain the timing of last year's Egyptian uprising, which took the regime of then-president Hosni Mubarak by surprise. At the time, the Egyptian economy was growing and poverty levels were among the lowest in the developing world, so the regime could reasonably have expected stability. In the decade leading up to the revolution, however, the country saw a quadrupling of graduates with no prospects — a marker of elite overproduction and hence, Turchin argues, trouble.