The American middle class is declining. As our middle class falls, our political temperature rises. Crane Brinton's likening of political revolution to a fever in his classic work "The Anatomy of Revolution" seems particularly apt. Middle-class decline is a preliminary symptom.

The diffusion or concentration of wealth underlies the most basic inflection points in political history: the diffusion of wealth in a middle class creates democracy; the concentration of wealth kills democracy.

Take it from the Romans: losing your middle class is a terrifically bad thing — unless you like being ruled by the rich. The late Roman Republic gives us an example that, in its general outlines, essentially parallels our current path.

Earlier this year, Martin Wolf invoked historical parallels in his piece "Donald Trump embodies how great republics meet their end." A few weeks later, Michael Tomasky referenced the increasingly-less-obscure namesake of our organization (Anacyclosis) in his article "The 2,100-Year-Old Word for Trumpism." A few months later, Andrew Sullivan drew upon Greek theory in arguing that Trump represents an "extinction-level event" for democracy in his article "America Has Never Been So Ripe for Tyranny."

Though we take no position with respect to any political campaign or candidate (or the conclusions in these articles), we applaud every honest effort to apply the lessons of history to explain political change; our organization — the Institute for Anacyclosis — was established to investigate the causality and recurrence of political revolution.

In keeping with that purpose, we submit the following as the key historical reference points:

Roman conquest of the Mediterranean basin led to the ruin of the agrarian middle class. By the time Carthage was defeated (149 B.C.), the yeoman farmers — the backbone of the republic ­— were exhausted from the demands of protracted military service. Moreover, they were unable or unwilling to compete with the influx of foreign grain and labor resulting from Roman conquest. Free labor was undercut by slave labor as the immense profits of empire, meanwhile, flowed into the hands of the rich. The wealthy exploited these conditions to create vast estates from the farms of the destitute yeomanry. Hence, alongside democracy arose plutocracy — rule by the wealthy.

The decline of the small farmers swelled the urban proletariat. The people grew increasingly miserable and dependent. Their dependency fueled a system of economic patronage. Meanwhile, many Romans jealously guarded their privileges, scorning proposals to extend citizenship to foreigners. The resulting animosity was a breeding ground for populist and reactionary demagogues, looming ever larger in the political landscape.

Despite the temptation to describe what followed with the classical term "ochlocracy" (mob rule), we think a degenerate democracy is better described as "demagarchy" — rule by popular leaders.

Demagarchy raged for a century until a single champion, Augustus, won this tournament of demagogues, emerging supreme from the ashes of the Republic. As emperor he tried to maintain the illusion that the Republic had been restored. But the Republic's fate had been sealed a century earlier, when wealth was concentrated in the rich and people were concentrated in the city. The Republic was doomed the moment its middle class was doomed.

Extreme social stratification always has been a prelude to revolution. An implacable conflict between few and many can only be resolved by one.

The essential forces sweeping the middle stratum off its feet in the 2nd century B.C. seem to be recurring in the 21st century A.D. The U.S., like the Roman Republic, achieved international hegemony. The Pax Americana (like the Pax Romana) both made the world a playground for the plutocracies of leading states.

And to whatever you attribute the cause — globalization and automation today (foreign grain and slave labor in antiquity) — the harmful effect is the same: oversupply of labor and falling wages, destabilizing the middle class.

Thus in America, as in Rome, the members of the ruined economic middle — dependent and xenophobic — may empower demagogues to lead them, who may undermine the republic. If American middle-class decline brings revolution in its train, the consequences will once again be felt the world around.

Timothy R. Ferguson is the founder and president of the Institute for Anacyclosis in Chapel Hill, N.C. David C. Gore is an associate professor of communication at the University of Minnesota Duluth and a director of the Institute for Anacyclosis. The views in this article are solely those of the authors.