Alfonso’s eldest son, Ferdinand de la Cerda, died before his father in a campaign against the Moors, who had attacked and defeated the governor of Algeciras in his fortified camp and conquered and slain the archbishop Sancho of Toledo, a brother of King Pedro III of Aragon, who marched against them (1275). A decree solemnly promulgated by the king in accordance with ancient Spanish law declared the second son Sancho heir to the throne, regardless of the fact that the dead man had left two sons, Ferdinand and Alfonso. But his widow, Blanche, daughter of St. Louis of France, now came forward in defence of her sons’ rights and her claims were powerfully supported both by her brother Philip III and by her stepmother Iolanthe, a sister of Peter III of Aragon. Thereupon a war ensued, which outlasted Alfonso’s reign and threw Castile into the greatest disorder and party strife. The king of France, with whom his sister sought refuge and help, took up the cause of his two nephews, now living in Aragon, and for several years conducted a destructive war against Alfonso on the borders of Navarre and Castile. The attempted intervention of the pope had no effect. The situation grew still worse when the king, having quarrelled with his son Sancho, wished to proceed to a partition. This plan was opposed by the members of the royal house and by a great part of the nobles. At an assembly at Valladolid Sancho was declared heir to the throne and regent, and invested with the government of the kingdom in his father’s stead (1282). Forsaken by his family and the estates, Alfonso called in the aid of Abu Yusuf of Morocco, while Sancho, disinherited and laid under a ban by his father in his turn, entered into an alliance with the emir of Granada. Thus, through the schism in the royal house, the power of the Moors in southern Spain was once more strengthened. At the same time the unhappy party wars in Castile itself led to the demoralisation of the people and the increase of the power of the nobles.[f]