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
Under the papacies of successive Popes smaller groups of Crusaders continued to travel to the Eastern Mediterranean to fight the Muslims and aid the Crusader States in the early 12thcentury. The third decade saw campaigns by Fulk V of Anjou, the Venetians, and Conrad III of Germany and the foundation of the Knights Templar. The period also saw the innovation of granting indulgences to those who opposed papal enemies, and this marked the beginning of politically motivated Crusades. The loss of Aleppo in 1128 and Edessa (Urfa) in 1144 to Imad ad-Din Zengi, governor of Mosul, led to preaching for what subsequently became known as the Second Crusade. King Louis VII and ConradIII led armies from France and Germany to Jerusalem and Damascus without winning any major victories. As in the First Crusade, the preaching led to attacks on Jews including massacres in the Rhineland, Cologne, Mainz, Worms and Speyer amid claims that the Jews were not contributing financially to the rescue of the Holy Land. Bernard of Clairvaux, who had encouraged the Second Crusade in his preaching, was so perturbed by the violence that he journeyed from Flanders to Germany to deal with the problem.