Why Did the Mongols Destroy Baghdad in 1258?

On February 13, 1258, Baghdad, then a city of 1 million, fell to the Mongols as the Abbasid Caliphate was destroyed. Tens of thousands were slaughtered ending the Islamic Golden Age. From the article:

"Why Did the Mongols Destroy Baghdad in 1258?

It took just thirteen days for the Ilkhanate Mongols and their allies to bring the Golden Age of Islam crashing down. Eye-witnesses reported that the mighty Tigris River ran black with ink from the precious books and documents destroyed along with the Grand Library of Baghdad, or Bayt al-Hikmah. Nobody knows for sure how many citizens of the Abbasid Empire died; estimates range from 90,000 to 200,000 up to 1,000,000. In two short weeks, the seat of learning and culture for the entire Muslim world was conquered and ruined.

Baghdad had been a sleepy fishing village on the Tigris before it was promoted to the status of the capital city by the great Abbasid caliph al-Mansur in 762. His grandson, Harun al-Rashid, subsidized scientists, religious scholars, poets, and artists, who flocked to the city and made it an academic jewel of the medieval world. The scholars and writers produced countless manuscripts and books between the late 8th century and 1258. These books were written on a new technology imported from China after the Battle of Talas River, a technology called paper. Soon, most of the people of Baghdad were literate and well-read.

Mongols Unite
Far to the east of Baghdad, meanwhile, a young warrior called Temujin managed to unite the Mongols and took the title Genghis Khan. It would be his grandson, Hulagu, who would push the boundaries of the Mongol Empire into what is now Iraq and Syria. Hulagu's primary purpose was to solidify his grip on the heartland of the Ilkhanate in Persia. He first completely annihilated the fanatical Shiite group known as the Assassins, destroying their mountain-top stronghold in Persia, and then marched south to demand that the Abbasids capitulate.

The Caliph Mustasim heard rumors of the Mongols' advance but was confident that the entire Muslim world would rise up to defend its ruler if need be. However, the Sunni caliph had recently insulted his Shiite subjects, and his own Shiite grand vizier, al-Alkamzi, may have even invited the Mongols to attack the poorly-led caliphate.

Late in 1257, Hulagu sent a message to Mustasim demanding that he open the gates of Baghdad to the Mongols and their Christian allies from Georgia. Mustasim replied that the Mongol leader should return to where he came from. Hulagu's mighty army marched on, surrounding the Abbasid capital, and slaughtering the caliph's army that sallied out to meet them.

The Mongols Attack
Baghdad held out for twelve more days, but it could not withstand the Mongols. Once the city's walls fell, the hordes rushed in and collected mountains of silver, gold, and jewels. Hundreds of thousands of Baghdadis died, slaughtered by Hulagu's troops or their Georgian allies. Books from the Bayt al-Hikmah, or House of Wisdom, were thrown into the Tigris, supposedly, so many that a horse could have walked across the river on them.

The caliph's beautiful palace of exotic woods was burned to the ground, and the caliph himself was executed. The Mongols believed that spilling royal blood could cause natural disasters like earthquakes. Just to be safe, they wrapped Mustasim in a carpet and rode their horses over him, trampling him to death.

The fall of Baghdad signaled the end of the Abbasid Caliphate. It was also the high point of Mongol conquest in the Middle East. Distracted by their own dynastic politics, the Mongols made a half-hearted attempt to conquer Egypt but were defeated at the Battle of Ayn Jalut in 1280. The Mongol Empire would grow no further in the Middle East."