The Byzantine emperor John II made Syrian expeditions twice, in the 1130s and 1140s. From the beginning of the twelfth century, the Syrian cities and the Crusader States preserved the balance of power through economic agreements and military alliances. However, Zangi, ruler of Aleppo, refused to maintain this balance-of-power policy and started to advance southward in Syria to recover lost territories from the Crusaders and obtain farmland which was under Damascus' rule. John carried out his expedition at this time.
John compelled Raymond of Poitiers, the consort of the heiress of Antioch, to become his liege vassal. John and Raymond agreed that Raymond would hand Antioch over to John in return for cities, currently in Muslim hands, which John would capture leading a joint Byzantine-Crusader army. But Raymond had John attack cities whose power Raymond himself wanted to reduce. Also, as the nobility of Antioch, who had come from south Italy, had influence over Raymond, John could not appoint a Greek Orthodox cleric as patriarch of Antioch. Furthermore, an encyclical issued by Pope Innocent II stating that all Latins serving in the Byzantine army were forbidden to attack Christians in Crusader States, forced John to reduce his claims on Antioch, being conscious of the West's eyes. John even sent messengers to Zangi investigating the possibility of forming an alliance with him if the nobility of Antioch rejected him.
John's Syrian expeditions largely changed the balance of power in Syria and made Zangi's advance in southern Syria easy. Zangi recaptured his lost territories, just after John retreated from besieging Shaizar, where Zangi had confronted him. The Byzantine threat and the reputation which Zangi gained as a strong leader made Damascus yield him Hims, which would be a base for his further advance southward in Syria.

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