The limited monarchy established by the Provisions of Oxford lasted only three years. Seeing the barons quarrelling among themselves, and Montfort accused of ambition and overweening masterfulness by many of his colleagues, the king took heart. Copying the example of his father in 1215, he obtained from the pope a bull, which declared the new constitution irregular and illegal, and absolved him from his oath to abide by it. He then began to recall his foreign friends and relatives, and to assemble mercenaries. De Montfort answered by raising an army, arresting prominent aliens, and seizing the lands which the king had given them. Henry thereupon, finding his forces too weak to face the earl, took refuge in the Tower of London and proposed an arbitration. He offered to submit his case to Louis IX., the saintly king of France, whose virtues were known and respected all over Europe, if the baronial party would do the same. An appeal to the pope they would have laughed to scorn; but the confidence felt in the probity of the French king was so great that Montfort advised his friends to accede to the proposal. This was an unwise step. Louis was a saint, but he was also an autocratic king, and had no knowledge of the constitutional customs of England. Having heard the claims of the king and the barons, he issued the mise of Amiens (Jan. 23, 1264), so called from the city at which he dated it, a document which stated that King Henry ought to abide by the terms of Magna Carta, to which he had so often given his assent, but that the Provisions of Oxford were wholly invalid and derogatory to the royal dignity. "We ordain," he wrote, "that the king shall have full power and free jurisdiction over his realm, as in the days before the said Provisions." The pope shortly afterwards confirmed the French king's award.
Simon de Montfort and his friends were put in an awkward position by this decision, to which they had so unwisely committed themselves. But they did not hesitate to declare that they must repudiate the mise. Simon declared that it would be a worse perjury to abandon his oath to keep the Provisions of Oxford than his oath to abide by the French king's award. He took arms again at the head of the Londoners and his personal adherents and allies. But many of the barons stood neutral, not seeing how they could refuse to accept the arbitration they had courted, while a number not inconsiderable joined the king, deciding that Leicester had passed the limits of reasonable loyalty, and that their first duty was to the crown.