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.
Islam in Palestine
In 1099, the Christian Crusaders, under the support of the Roman Catholic Church, launched the First Crusade campaign with the aims of regaining control of Jerusalem from the Islamic Empire, and helping the Byzantine Empire fight the Seljuk Turks. During the campaign, the Crusaders launched an assault on the city of Jerusalem, captured it in July 1099, massacring many of the city's Muslim and Jewish inhabitants, and established the first Christian Kingdom of Jerusalem. The Crusaders transformed the Dome of the Rock into the "Shrine of the Lord" (Templum Domini) and the Al-Aqsa mosque into the "Hall of Solomon" (Templum Solomonis). The local Muslim reaction was to try to find an accommodation with the Crusaders. During this era, the larger Muslim world looked upon the setbacks in Jerusalem with indifference.