This short lecture on history is about the fall of the once mighty caliphate of Baghdad when Mongolian horsemen invaded and destroyed its capital and killed the last ruler of the Abasside dynasty.
In the 13th century, the Mongols finally decided to repel the Muslims who had been making incursions from Kazakhstan into Western Mongolia and China for six hundred years.
In 1257, Hulagu, a grandson of Mongolia's famous leader Ghengis Khan, asked the Abasside Caliph al-Mutasim, the 37th of his dynasty, to recognize Mongol sovereignty or perish. Hulagu's claim was based on an ancient agreement between al-Mutasim's predecessors and the Seljuk Turks who were of a clan distantly related with the Mongols. That agreement comprised supremacy of Seljuk rulers over the Abasside caliphate in Baghdad.
The Caliph who called himself "prince of the faithful" sent word to Hulagu Khan that any attack on his capital would mobilize the entire Muslim world from India to north-west Africa. Not in the least impressed by his enemy's overconfidence, Ghengis Khan's successor announced his intention of taking the city of Baghdad by force. It was in 1258 that Hulagu and his huge army of Mongolian horsemen finally succeeded in overrunning the caliphate's defense.
The cruel death of Caliph al-Mutasim and the downfall of his empire, comprising far more than Iraq and Syria, showed repercussions everywhere in the Islamic world and led to a temporary decline of Islamic culture.
In 1258, Mongolian horsemen didn't need the U.S. Cavalry.
Mongolia - The Art of War
Therefore I say: Know your enemy and know yourself, and you can fight a hundred battles without peril. If you are ignorant of the enemy and know only yourself, you will stand equal chances of winning and loosing. If you know neither the enemy nor yourself, you are bound to be defeated in every battle.