The longer cycle is "the one which we understand much better, and it is a universal feature of all complex societies," Turchin told Life's Little Mysteries. From the Roman Empire to medieval France to ancient China, scholars have noted that societies swing between 100-150 years of relative peace and 100-150 years of conflict, and then back again. Only some societies exhibit the shorter-term, and less subtle, 50-year-long cycles of violence along the way — the Roman Empire, for one, and if Turchin's theory is correct, the United States as well.
Why 50-year cycles? Turchin explained that a surge of violence begins in the same way as a forest fire: explosively. After a period of escalation followed by sustained violence, citizens begin to "yearn for the return of stability and an end to fighting," he wrote in his paper. The prevailing social mood swings toward stifling the violence at all costs, and those who directly experienced the civil violence maintain the peace for about a human generation — 20 or 30 years. But the stability doesn't last.
Eventually, "the conflict-scarred generation dies off or retires, and a new cohort arises, people who did not experience the horrors of civil war and are not immunized against it. If the long-term social forces that brought about the first outbreak of internal hostilities are still operating, then the society will slide into the second civil war," he wrote. "As a result, periods of intense conflict tend to recur with a period of roughly two generations (40–60 years)."
