THE Coptic Orthodox Church in Egypt is one of the oldest Christian communities in the world, tracing its roots to St. Mark the apostle and the first century A.D. Coptic Christians have survived persecutions and conquests, the fall of Rome and the rise of Islam. They have been governed from Constantinople and Ctesiphon, Baghdad and London. They have outlasted the Byzantines, the Umayyads and the Ottomans, Napoleon Bonaparte and the British Empire.

But they may not survive the Arab Spring.

Apart from Hosni Mubarak and his intimates, no group has suffered more from Egypt’s revolution than the country’s eight million Copts. Last week two dozen people were killed in clashes between the Coptic Christians and the Egyptian Army, a grim milestone in a year in which the Coptic community has faced escalating terrorist and mob violence. A recent Vatican estimate suggests that 100,000 Copts may have fled the country since Mubarak’s fall. If Egypt’s Muslim Brotherhood consolidates political power, that figure could grow exponentially.

This is a familiar story in the Middle East, where any sort of popular sovereignty has tended to unleash the furies and drive minorities into exile. From Lebanon to North Africa, the Arab world’s Christian enclaves have been shrinking steadily since decolonization. More than half of Iraq’s 1.5 million Christians have fled the country since the American invasion toppled Saddam Hussein.

More important, though, this is a familiar story for the modern world as a whole — a case of what National Review’s John Derbyshire calls “modernity versus diversity.” For all the bright talk about multicultural mosaics, the age of globalization has also been an age of unprecedented religious and racial sorting — sometimes by choice, more often at gunpoint. Indeed, the causes of democracy and international peace have often been intimately tied to ethnic cleansing: both have gained ground not in spite of mass migrations and mass murders, but because of them.