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.
First Crusade
The four main crusader armies left Europe around the appointed time in August 1096. They took different paths to Constantinople and gathered outside its city walls between November 1096 and April 1097; Hugh of Vermandois arrived first, followed by Godfrey, Raymond, and Bohemond. This time, Emperor Alexios was more prepared for the crusaders; there were fewer incidents of violence along the way.