northern frontier. Henry knighted Alexander III before the young king married Henry's daughter Margaret in 1251 and, despite Alexander's refusal to give homage to Henry for Scotland, the two enjoyed a good relationship. Henry had Alexander and Margaret rescued from Edinburgh Castle when they were imprisoned there by a rebellious Scottish baron in 1255 and took additional measures to manage Alexander's government during the rest of his minority years. European strategy Henry had no further opportunities to reconquer his possessions in France after the collapse of his military campaign at the Battle of Taillebourg. Henry's resources were quite inadequate in comparison to those of the French Crown, and by the end of the 1240s it was clear that King Louis had become the preeminent power across France. Henry instead adopted what historian Michael Clanchy has described as a "European strategy", attempting to regain his lands in France through diplomacy rather than force, building alliances with other states prepared to put military pressure on the French King. In particular, Henry cultivated Frederick II, hoping he would turn against Louis or allow his nobility to join Henry's campaigns. In the process, Henry's attention became increasingly focused on European politics and events rather than domestic affairs. Crusading was a popular cause in the 13th century, and in 1248 Louis joined the ill-fated Seventh Crusade, having first made a fresh truce with England and received assurances from the Pope that he would protect his lands against any attack by Henry. Henry might have joined this crusade himself, but the rivalry between the two kings made this impossible and, after Louis's defeat at the Battle of Al Mansurah in 1250, Henry instead announced that he would be undertaking his own crusade to the Levant. He began to make arrangements for passage with friendly rulers around the Levant, imposing efficiency savings on the royal household and arranging for ships and transport: he appeared almost over-eager to take part. Henry's plans reflected his strong religious beliefs, but they also stood to give him additional international credibility when arguing for the return of his possessions in France. Henry's crusade never departed, as he was forced to deal with problems in Gascony, where the harsh policies of his lieutenant, Simon de Montfort, had provoked a violent uprising in 1252, which was supported by King Alfonso X of neighbouring Castile. The English court was split over the problem: Simon and