 Complete the following phrase:  Michaels response to the Treaty of Viterbo was to attempt to weaken papal support for it; if the Pope was convinced Charles of Anjous invasion was a just and holy war, then the forces Michael could call on could not prevent its success. Michael returned to negotiating a union of the churches with Pope Clement IV, which he had agreed to, but the latters death in November 1268 put an end to this approach. According to Geanakoplos, only a lack of resources prevented Charles from immediately launching an attack against Michael. Looking for some restraint on Charles, Michael made a shrewd appeal to King Louis IX of France, the leading ruler of the West and the elder brother of Charles. Louis was more interested in a crusade against Muslims controlling the Holy Land than attacking a schismatic Christian. So he had Charles join his 