A Deal with Death. What if the Franco-Mongolian alliance had gone through?
Point of Divergence
In the 1200s several attempts at a Franco-Mongol alliance against the Islamic caliphates, their common enemy, were made by various leaders among the Frankish Crusaders and the Mongol Empire. Such an alliance might have seemed an obvious choice: the Mongols were already sympathetic to Christianity, given the presence of many influential Nestorian Christians in the Mongol court. The Franks (Western Europeans and those in the Crusader States of the Levant) were open to the idea of support from the East, in part owing to the long-running legend of the mythical Prester John, an Eastern king in a magical kingdom who many believed would one day come to the assistance of the Crusaders in the Holy Land. The Franks and Mongols also shared a common enemy in the Muslims. However, despite many messages, gifts, and emissaries over the course of several decades, the often-proposed alliance never came to fruition.
Contact between Europeans and Mongols began around 1220, with occasional messages from the papacy and European monarchs to Mongol leaders such as the Great Khan, and subsequently to the Ilkhans in Mongol-conquered Iran. Communications tended to follow a recurring pattern: the Europeans asked the Mongols to convert to Western Christianity, while the Mongols responded with demands for submission and tribute. The Mongols had already conquered many Christian and Muslim nations in their advance across Asia, and after destroying the Muslim Abbasid and Ayyubid dynasties, for the next few generations fought the remaining Islamic power in the region, the Egyptian Mamluks. Hethum I, king of the Christian nation of Cilician Armenia, had submitted to the Mongols in 1247, and strongly encouraged other monarchs to engage in a Christian-Mongol alliance, but was only able to persuade his son-in-law, Prince Bohemond VI of the Crusader State of Antioch, who submitted in 1260. Other Christian leaders such as the Crusaders of Acre were more mistrustful of the Mongols, perceiving them as the most significant threat in the region. The Barons of Acre therefore engaged in an unusual passive alliance with the Muslim Mamluks, allowing Egyptian forces to advance unopposed through Crusader territory to engage and defeat the Mongols at the pivotal Battle of Ain Jalut in 1260.
European attitudes began to change in the mid-1260s, from perceiving the Mongols as enemies to be feared, to potential allies against the Muslims. The Mongols sought to capitalize on this, promising a re-conquered Jerusalem to the Europeans in return for cooperation. Attempts to cement an alliance continued through negotiations with many leaders of the Mongol Ilkhanate in Iran, from its founder Hulagu through his descendants Abaqa, Arghun, Ghazan, and Öljaitü, with surprising success. The Mongols invaded various Muslim controlled lands several times between 1281 and 1312, in joint operations with the Franks and various other Christian kingdoms, but the considerable logistical difficulties involved meant that forces would arrive months apart, they were able to push the Muslims due to the amount of Christian Crusaders and Mongolian forces pushing into the region. When the Mongols eventually devolved into civil war, the once declining Byzantines marched to reclaim and conquer the weakened Muslim lands. The Byzantines were not the only ones to go on to reclaim the lands, the Crusaders states eventually united under the Christian banner of the Kingdom of Jerusalem.