The new vows of Frederick were strengthened by his marriage with the heir of the king of Jerusalem. The marriage was celebrated at Rome, amidst the benedictions of the clergy and the acclamations of the people; all the Christians of the West heard of it with joy, and this union appeared to them to be the most certain pledge of the victories the Crusaders would gain over the infidels. John of Brienne, who assisted at the ceremony, congratulated himself upon having obtained an emperor for a son-in-law and a supporter; but his joy was not of long duration. Frederick, after his marriage, only saw in him the brother of that Gauthier de Brienne, who had borne the title of king of Naples and Sicily; he considered him as an enemy to his power, a dangerous rival, and he disputed the possession of the kingdom of Jerusalem with him. The pope was secretly pleased at this claim or pretension, as he hoped it would promote the interests of the crusade. Honorius was delighted to see the ambition of the emperor mix itself up with the great designs for the execution of which he was so anxious. Frederick was therefore acknowledged king of Jerusalem. Thus John of Brienne, who had always proved himself the most ardent apostle of the holy war, deprived of his crown, and from that time a stranger to the affairs of Palestine, was obliged to wait in retirement and silence for a favourable opportunity to avenge himself on his son-in-law, and recover his kingdom. Frederick carried on his preparations for the holy war, and appeared more than ever disposed to set out for the East. The crusade was preached, in the name of the head of the Church, in all the kingdoms of Europe; the sovereign pontiff wrote to the princes to exhort them to suspend their divisions and occupy themselves solely with the war beyond the sea. As hostilities had just been renewed between England and France, Honorius ordered Louis VIII. to lay down his arms, and threatened him with excommunication, if he did not immediately make peace. The king of France, before he obeyed the orders of the pope, was desirous of completing the conquest of Poitou; and whilst the thunders of Rome were growling over his head, the people and clergy were returning Heaven thanks for his victories, in every church of his kingdom.