 On April 10 , 1262 , the Mongol leader Hulagu sent through John the Hungarian a new letter to King Louis IX of France , again offering an alliance . The letter explained that previously , the Mongols had been under the impression that the pope was the leader of the Christians , but now they realized that the true power rested with the French monarchy . The letter mentioned Hulagu 's intention to capture Jerusalem for the benefit of the pope , and asked for Louis to send a fleet against Egypt . Hulagu promised the restoration of Jerusalem to the Christians , but also still insisted on Mongol sovereignty , in the Mongols ' quest for conquering the world . It is unclear whether or not King Louis actually received the letter , but at some point it was transmitted to Pope Urban , who answered in a similar way as his predecessors . In his papal bull Exultavit cor nostrum , Urban congratulated Hulagu on his expression of goodwill towards the Christian faith , and encouraged him to convert to Christianity . 
