Michael's response to the Treaty of Viterbo was to attempt to weaken papal support for it; if the Pope was convinced Charles of Anjou's 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 latter's 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 Tunisian crusade in 1270. When Louis died in Tunisia, Charles took command, negotiated a truce, and sailed to Sicily, planning to attack Byzantium. At this point a miracle saved Michael: a violent storm destroyed Charles' fleet. "To the Greeks of Byzantium," writes Geanakoplos, "it must have seemed as if the Virgin, their protector, had saved them from disaster."