The last Abbasid caliph disbanded his army to save money — the Mongols took Baghdad

By the mid-13th century the Abbasid Caliphate was a shadow of its former self — still the spiritual center of Sunni Islam but militarily weak and politically isolated. Caliph Al-Musta'sim, the 37th Abbasid caliph, was described by contemporaries as indecisive, easily swayed by his courtiers, and above all frugal to the point of folly. He hoarded treasure while his army crumbled, believing that gold was the surest defense.

When Hulagu Khan, grandson of Genghis Khan, marched westward with the Mongol army in 1257, he sent envoys to Baghdad demanding submission. The Caliph's advisors — especially his vizier Ibn al-Alqami — urged him to negotiate, pay tribute, and prepare the city's defenses. Al-Musta'sim refused. He boasted that the caliphate had stood for 500 years and that the Mongols would tire before Baghdad's walls. He cut military spending and dismissed urgent warnings.

Hulagu's army reached Baghdad in January 1258: perhaps 150,000 soldiers with siege engines, engineers, and a fleet of boats to cross the Tigris. The Caliph belatedly raised a force of 50,000, but they were untrained and poorly led. A sortie was crushed when the Mongols broke the dikes and flooded the plain. On 10 February the Caliph surrendered. Hulagu executed him by wrapping him in a carpet and trampling him with horses — a Mongol taboo against spilling royal blood.

The sack lasted a week. Mosques, libraries, and palaces were burned. The House of Wisdom — Baghdad's great library, repository of centuries of Persian, Greek, and Indian knowledge — was destroyed, its books thrown into the Tigris until the river ran black with ink. Estimates of the dead range from 200,000 to over a million. The Abbasid Caliphate, which had ruled the Islamic world since 750, was extinguished. Baghdad would not recover for centuries.