This is supposed to be a challenge?
Easy, during the 7th Crusade the Mongol Khan Mongke accepts King Louis' invitation to convert to Christianity and issues an order, everyone in his Empire was to convert as well, in an unChristian-like manner Mongke proclaimed anyone who refuses to convert will be beheaded. The religion spreads like wildfire throughout the Mongol Empire, and the Muslim's now have a new Christian enemy trying to reclaim the Holy Land. Unfortunatley for the Muslim's the Mongols and European Christians are too powerful of a force to fight off. Mongke takes the Crusades to not only conquer the Holy Land, but Arabia as well. The campaign against the Muslims of Arabia lasts 100 years when Mecca and Medina are finally sacked by the Mongol Christians.
After the fall of the Holy Cities, Islam began to fade into only pockets of desert dwellers. Arabia becomes Christian following the Coptic Churches doctrine. Another Great Schism divides the Mongol Christians from the western European Christians. The Mongols develop what becomes known as Mongolian Orthodox and embarks on another crusade against India and Southeast Asia. Mongolia's final crusade would be in failure as it attempted to gain a foothold on Japan.