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
The 20th century produced three important histories of the Crusades: one by Steven Runciman, another by Rene Grousset, and a multi-author work edited by Kenneth Setton. Historians in this period often echoed Enlightenment-era criticism: Runciman wrote during the 1950s, "High ideals were besmirched by cruelty and greed ... the Holy War was nothing more than a long act of intolerance in the name of God". According to Norman Davies, the Crusades contradicted the Peace and Truce of God supported by Urban and reinforced the connection between Western Christendom, feudalism, and militarism. The formation of military religious orders scandalised the Orthodox Byzantines, and Crusaders pillaged countries they crossed on their journey east. Violating their oath to restore land to the Byzantines, they often kept the land for themselves. The Fourth Crusade is widely considered controversial in its "betrayal" of Byzantium. Similarly, Norman Housley viewed the persecution of Jews in the First Crusadea pogrom in the Rhineland and the massacre of thousands of Jews in Central Europeas part of the long history of anti-Semitism in Europe.