The Mongols followed the policy of killing any religious leader who claimed an authority higher than the Great Khan. Genghis Khan had Teb Tengeri, the preacher of Mongolian religion of Sky God, killed. When Hulagu Khan, Genghis Khan’s grandson, captured Baghdad in 1258, he killed the Caliph of Baghdad.
The Mongols tried to summon the Pope to their court for observing his attitude towards the Great Khan. If the Pope had accepted their invitation, they might have killed him.
On March 13, 1245, Pope Innocent IV wrote a letter called “cum non solum” to the Great Khan, demanding that the Mongols should desist from attacking Christians. The Pope inquired about the future plans of the Mongol Empire, and expressed the hope that there would be peace between the Mongols and the Christians. He was probably unaware that the word “peace” was a synonym for “subjugation” in the Mongol language.
A papal delegation, led by Giovanni da Pian del Carpine (also known as John of Plano Carpini), made a perilous journey of more than three thousand miles and brought the Pope’s letter to Karakorum, the capital of the Mongol Empire, in July 1246. After a month of waiting, they had an audience with Güyük Khan, then the Great Khan (he was the son of Genghis Khan’s eldest son Ögedei Khan).
In November 1246, the papal delegation was allowed to leave Karakorum with a response in Mongol, Latin, and Arabic from the Great Khan. Towards the end of 1247, they found the Pope in Lyon and delivered to him their report and the Great Khan's letter.
Güyük Khan’s imperiously worded letter to the Pope begins with a preamble, which is translated as: “We, by the power of the eternal heaven, Khan of the great Ulus, Our command.” The letter declares that the office of the Great Khan is the scourge of God and it makes the following demand from the Pope:
"You must say with a sincere heart: "We will be your subjects; we will give you our strength". You must in person come with your kings, all together, without exception, to render us service and pay us homage. Only then will we acknowledge your submission. And if you do not follow the order of God, and go against our orders, we will know you as our enemy.”
Just as the Mongols did not tolerate any rival monarch, they did not tolerate any rival religious leader. Genghis Khan and the Khans who followed him were the God’s true representatives on earth. To defy the Great Khan was to disobey God.