The New York Review of Books

Late in the year 1818, the people of Constantinople witnessed the execution of a bandit chief who had been captured in the arid badlands of Arabia. Tried and convicted by the Ottoman Empire’s highest sharia court for heresy as well as brigandage, the rebel was dragged to the gate of the sultan’s palace. The decapitation itself was swift, but his severed head was then placed in a giant mortar and ceremoniously pounded into pulp; his body spiked on a tall pole and displayed, a sunken dagger pinning the sentence of irtidad—excommunication—to his bloodied chest for all to see.

The unfortunate Arab chieftain happens to have been an Al Saud,

The Al Sauds had been petty chiefs of a particularly poor, remote patch of central Arabia near the modern city of Riyadh when, sometime in the 1740s, the chance came of allying themselves with a revivalist preacher named Muhammad ibn Abdul Wahhab. The fusion of Saudi sword and Wahhabist fervor, still commemorated in the modern kingdom’s flag, elevated the Al Sauds’ ambitions from mere tribal raids into a full-scale jihad. Within two generations they had succeeded in conquering most of the Arabian peninsula, uniting the territory for the first time since the initial expansion of Islam a thousand years earlier.

But the early Saudis pushed things too far. In 1801 they sacked the Shia holy city of Karbala in Iraq, destroying its gold-domed shrines, slaughtering thousands of its inhabitants, and carrying off wives, daughters, and possessions. Such booty was theirs by assumed right, since the Wahhabists’ ultra-Sunnism taught that the Shia could not claim to be fellow Muslims. Their veneration of tombs was held to be a form of idolatry, a sin punishable by death. So when, in 1806, the Saudis overran the Ottoman garrisons of Mecca and Medina, cities holy to Sunnis and Shias alike, they again smashed every tomb they could find, forcibly applied their strict rules, and whipped, robbed, or murdered pilgrims who disobeyed.

At last, in 1811, the Ottoman sultan responded, delegating the powerful Wali of Egypt, Muhammad Ali Pasha, to dispose of this nuisance. His well-equipped army quickly recaptured the Hijaz, the region of the holy cities. But the campaign into the barren heart of Arabia was grueling. Fierce Saudi resistance led the invaders to adopt scorched-earth tactics. By the time the emir Abdallah surrendered, half the villages of central Arabia had been burned to the ground, their wells poisoned, their palms uprooted, their herds scattered. Some four hundred …