The rulers of the Islamic world in the 1200s were not born into aristocracy or priesthood, as was the custom in Europe. They were an army of former slaves. Trained in combat and Sunni Islam from a young age, these "Mamluks" (from the Arabic for "property") soon grew so vast in number that they wrested control of the Empire from the Abbasid Caliphs — one of very few times in history.
During the Crusades, it was Mamluks who met the Crusaders as they attempted to retake the Holy Land for Christendom. But the most important imprint the Mamluks have on history is a single battle that took place in modern-day Israel that meant the difference between centuries of rule and utter annihilation.
In the 13th Century, a wave of destruction flowed across Asia and into Europe. The Mongols, an amalgamation of far-east tribes and clans from the Mongolian Plateau, united their people, reorganized their armies, and began to expand their controlled territory.
The Mongols began to expand under Genghis Khan, and that expansion continued long after his death. For over 100 years, the Mongol armies swept South and West, demanding immediate surrender and destroying and slaughtering those who didn't submit.
They didn't suffer a real defeat until more than 60 years into the conquest at the Battle of Ain Jalut, near the Sea of Galilee — at the hands of the Mamluks.
The Mongols' loss at Ain Jalut shattered the image of Mongol invincibility and slowed their advance so much they actually had to retreat from the Levant. The Mamluk victory kept the Mongols from taking Cairo and sweeping into Africa.
The Mamluks continued to rule the Islamic world for centuries, where they were subsumed by the emerging Ottoman Empire — though they remained influential in the Empire for centuries afterward, even fighting both Napoleon and U.S. Marines (but losing to both).
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