The size of Frederick II's army and his reputation within the Islamic world was sufficient to regain Jerusalem, Bethlehem, Nazareth and a number of neighbouring castles without violence. These were recovered by treaty from the AyyubidSultanAl-Kamil. However, Jerusalem did not remain for long in Christian hands, as there was not enough Christian-held hinterland to make it defensible.
The Ayyubids invited the free-roaming Khwarazmian clans, whose empire had been destroyed by the Mongols, to reconquer the city. In the siege and subsequent fall of the city on July 15, 1244, the Khwarezmians completely razed Jerusalem, leaving it in ruins and useless to both Christians and Muslims. The Seventh Crusade under Louis IX of France was motivated by this massacre, but it accomplished little except to play a part in the process of replacement of the Ayyubid sultans with the more powerful Mamluks, who were the Crusaders' main opponents in 1250.