The Mongol invasion of Europe ended in 1242, in part because of the death of the Great Khan Ögedei, successor to Genghis Khan. When one Great Khan died, Mongols from all parts of the empire were recalled to the capital to decide who should be the next Great Khan. In the meantime, the Mongols' relentless march westward had displaced the Khawarizmi Turks, who themselves moved west, eventually allying with the Ayyubid Muslims in Egypt. Along the way, the Turks took Jerusalem from the Christians in 1244. After the subsequent loss at the Battle of La Forbie, Christian kings began to prepare for a new crusade (the Seventh Crusade), declared by Pope Innocent IV in June 1245 at the First Council of Lyon. The loss of Jerusalem caused some Europeans to look to the Mongols as potential allies of Christendom, provided the Mongols could be converted to Western Christianity. In March 1245, Pope Innocent IV had issued multiple papal bulls, some of which were sent with an envoy, the Franciscan John of Plano Carpini, to the "Emperor of the Tartars". In a letter now called the "Cum non solum", Pope Innocent expressed a desire for peace, and asked the Mongol ruler to become a Christian and to stop killing Christians. However, the new Mongol Great Khan Güyük, installed at Karakorum in 1246, replied only with a demand for the submission of the pope, and a visit from the rulers of the West in homage to Mongol power: