Military history of the Crusader states
The Seljuk–Crusader War began when the First Crusade wrested territory from the Seljuk Turks during the Siege of Nicaea in 1097 and lasted until 1128 when Zengi became atabeg of Aleppo. At the latter date, the chief threat to the Crusaders from the east and north became the Zengids. The conflict was generally fought between European Crusaders and the Seljuk Turks and their vassals. The Muslim Syrian emirates occasionally allied themselves with the Christians against rival states.
Barons' Crusade
This crusade to the Holy Land is sometimes discussed as two separate crusades: that of King Theobald I of Navarre, which began in 1239; and, the separate host of crusaders under the leadership of Richard of Cornwall, which arrived after Theobald departed in 1240. Additionally, the Barons' Crusade is often described in tandem with Baldwin of Courtenay's concurrent trip to Constantinople and capture of Tzurulum with a separate, smaller force of crusaders. This is because Gregory IX briefly attempted to redirect the target his new crusade from liberating the Holy Land from Muslims to protecting the Latin Empire of Constantinople from heretical Christians.