Islam
Islam in the later 12th Century
Before talking about the Mongols directly, I'm going to back up a bit and talk about other developments in Islam, starting in the later 12th century. The Mongol invasions were of paramount importance in the 13th century, but to get a good picture of this, we need to consider the Muslim world more broadly than from Cairo and Damascus.
Saladin accomplished much more than replacing the Fatimid dynasty with his own. His brother Turanshah subjugated Nubia and conquered the Yemen in the 1170s. Saladin himself brought Mosul under his sway in 1186. This brought Ayyubid interests into contact with Persia, Armenia and Georgia, and the Indian Ocean.
Saladin was a Sunni Muslim, and his overthrow of the Shi'ite Fatimids greatly angered the Assassins. Rashid al-Din Sinan (1163-1193), known as the Old Man of the Mountain, was Saladin's inveterate enemy. Twice his men penetrated into Saladin's own tent. One even succeeded in wounding the Sultan. More significantly, the Assassins became a great power in their own right in Persia and Syria, and their enmity thwarted Saladin's plans more than once.
In Baghdad, the Caliphate enjoyed a resurgence of authority under Nasir (1180-1225). He made alliances with the Alids and with the Isma`ili Imam at Alamut (Sinan), consciously trying to heal the schism between Shi'a and Sunni. He also opposed the Khwarizmian Turks, who had succeeded the Seljuks in Asia Minor and who now were trying to make Nasir subject to them. The Khwarismians themselves were great warriors, and they recruited heavily among the Kipchak tribes of the lower Volga, the same tribes that provided Egypt its Mameluks. Their leader took the old Persian title of Shah, and it was Muhammad Shah (1200-1220) who was leading the drive on Baghdad.
In 1217, Muhammad Shah succeeded in driving Nasir out of Baghdad, bringing one of the Alid family in to serve as a properly obedient and harmless Caliph. He was at the height of his power, but he was not to enjoy it for very long.
In 1218, a caravan of merchants arrived at Utrar, on the Persian frontier. The Khwarismians by this time had conquered Transoxiana as well, bringing them into direct contact with the tribes of Russia. The governor of the town claimed these merchants were spies and had them executed. This was a mistake, for the merchants (spies or not) had come from the land of the Mongols and were under the protection of one Ghengis Khan. When the Great Khan learned of the incident, he swore revenge. The days of the Khwarismians were numbered, and Islam was about to be invaded by the Mongol hordes.