In 1238, the European kings Louis IX of France and Edward I of England rejected the offer of the Nizari Imam Muhammad III of Alamut and the Abbasid caliph Al-Mustansir for a Muslim–Christian alliance against the Mongols. They later joined the Mongols against all Muslims. Military collaboration between the Mongols and their Christian vassals became substantial in 1258–1260. Hulagu's army, with the forces of his Christian subjects Bohemond VI of Antioch, Hethum I of Armenia, and the Christian Georgians, effectively destroyed two of the most powerful Muslim dynasties of the era: the Abbasids in Baghdad and the Ayyubids in Syria.