Finally, [the Mongol ruler] Il-Khan Ghazan (ruled 1295-1304), who converted from Buddhism to Islam, offered the Western European rulers Pope Boniface VIII, King Edward I of England and James II of Aragon his conversion to Christianity in the case of a military alliance against the arch-enemy Egypt.
But the age of the Crusades had passed and Acre, the last Christian bastion of Palestine, had fallen in 1291. In 1287 the kings Philip the Fair of France and Edward I of England had given the cold shoulder to Rabban Bar Sauma, the Nestorian special envoy of Il-Khan Arghun. Even though the mission brought no results, it testifies to the international character of the Church of the East at that time that the Ongut Rabban Bar Sauma, who had lived in a monastic cell south of today’s Beijing, came to Baghdad and later traveled to Italy and France, becoming a kind of Asian Marco Polo in reverse.
In light of the lack of European interest in an anti-Islamic alliance, Ghazan remained a Muslim. Thus a window of opportunity for a possible re-Christianization of the region that is today Iran and Iraq closed forever.Baumer, The Church of the East, p. 5