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.
Crusades
From the 8th century, the Christians entered to recapture the Iberian peninsula from the Muslims, known as the "Reconquista". The campaign reached a  turning point in 1085 when Alfonso VI of León and Castile captured Toledo. In the same period, the Muslim Emirate of Sicily was conquered by Norman adventurer Roger de Hauteville in 1091.