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.
Siege of Edessa (1144)
The County of Edessa was the first of the crusader states to be established during and after the First Crusade. It dates from 1098 when Baldwin of Boulogne left the main army of the First Crusade and founded his own principality.