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.
Historiography of the Crusades
Steven Runciman's three volume "History of the Crusades" (1951–54) marks a turn from the idealization of the Crusades as heroic enterprise in the 19th century to their denunciation as "a barbarian invasion", primarily of the Byzantine Empire, among a current of historiography of the second half of the 20th century.
Peters (2011) says that Runciman's work "instantly became the most widely known and respected single-author survey of the subject in English." 
Madden (2005) stresses the impact of Runciman's style and viewpoint: as having "single-handedly crafted the current popular concept of the crusades" by painting the crusaders as "simpletons or barbarians".