Unification of The Sultanate
It was Nur ad-Din's dream to unite the various Muslim forces between the Euphrates and the Nile to make a common front against the crusaders. In 1149 Saif ad-Din Ghazi died, and a younger brother, Qutb ad-Din Mawdud, succeeded him. Qutb ad-Din recognized Nur ad-Din as overlord of Mosul, so that the major cities of Mosul and Aleppo were united under one man. Damascus was all that remained as an obstacle to the unification of Syria.
After the failure of the Second Crusade, Mu'in ad-Din had renewed his treaty with the crusaders, and after his death in 1149 his successor Mujir ad-Din followed the same policy. In 1150 and 1151 Nur ad-Din besieged the city, but retreated each time with no success, aside from empty recognition of his suzerainty. When Ascalon was captured by the crusaders in 1153, Mujir ad-Din forbade Nur ad-Din from travelling across his territory. Mujir ad-Din, however, was a weaker ruler than his predecessor, and he also agreed to pay an annual tribute to the crusaders in exchange for their protection. The growing weakness of Damascus under Mujir ad-Din allowed Nur ad-Din to overthrow him in 1154, with help from the population of the city. Damascus was annexed to Zengid territory, and all Syria was unified under the authority of Nur ad-Din, from Edessa in the north to the Hauran in the south. He was cautious not to attack Jerusalem right away, and even continued to send the yearly tribute established by Mujir ad-Din; meanwhile he briefly became involved in affairs to the north of Mosul, where a succession dispute in the Sultanate of Rüm threatened Edessa and other cities.
In 1157 Nur ad-Din besieged the Knights Hospitaller in the crusader fortress of Banias and routed a relief army from Jerusalem, but he fell ill that year and the crusaders were given a brief respite from his attacks. In 1159 the Byzantine emperor Manuel I Comnenus arrived to assert his authority in Antioch, and the crusaders hoped he would send an expedition against Aleppo. However, Nur ad-Din sent ambassadors and negotiated an alliance with the emperor against the Seljuks, much to the crusaders' dismay. Nur ad-Din, along with the Danishmends of eastern Anatolia, attacked the Seljuk sultan Kilij Arslan II from the east the next year, while Manuel attacked from the west. Later in 1160, Nur ad-Din captured the Prince of Antioch, Raynald of Châtillon after a raid in the Anti-Taurus mountains; Raynald remained in captivity for the next sixteen years. By 1162, with Antioch under nominal Byzantine control and the crusader states further south powerless to make any further attacks on Syria, Nur ad-Din made a pilgrimage to Mecca. Soon after he returned, he learned of the death of King Baldwin III of Jerusalem, and out of respect for such a formidable opponent he refrained from attacking the crusader kingdom: William of Tyre reports that Nur ad-Din said "We should sympathize with their grief and in pity spare them, because they have lost a prince such as the rest of the world does not possess today."
Read more about this topic: Nur Ad-Din Zangi