Frederick II, Holy Roman Emperor led the Sixth Crusade to the Holy Land in 1228, and claimed the kingship of Jerusalem by right of his wife, Queen Yolande of Jerusalem, who had inherited the title of 'Queen of Jerusalem' from her mother, Maria of Montferrat, the wife of John of Brienne.
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 with the Ayyubid Sultan Al-Kamil. However, Jerusalem did not remain for long in Christian hands, as there was not enough territory around it in Christian hands to make it defensible.
The Ayyubids invited the Khwarezmian clans 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 replace the Ayyubids and Khwarezmians with the more powerful Mamluks as the Crusaders' main opponents in 1250.
- The Siege on Orthodox Wiki
- The Siege on Encyclopædia Britannica
- The Siege on Timeline:History of Jerusalem
- The Siege on The Jewish History Resource Center