War against Crusaders
Nur ad-Din was the second son of Imad ad-Din Zengi, the Turkish atabeg of Aleppo and Mosul, who was a devoted enemy of the crusader presence in Syria. After the assassination of his father in 1146, Nur ad-Din and his older brother Saif ad-Din Ghazi I divided the kingdom between themselves, with Nur ad-Din governing Aleppo and Saif ad-Din Ghazi establishing himself in Mosul. The border between the two new kingdoms was formed by the Nahr al-Khabur River. Almost as soon as he began his rule, Nur ad-Din attacked the Principality of Antioch, seizing several castles in the north of Syria, while at the same time he defeated an attempt by Joscelin II to recover the County of Edessa, which had been conquered by Zengi in 1144. (See Siege of Edessa.) In 1146, after the Frankish attempt to reoccupy Edessa, Nur ad-Din massacred the local Armenian Christian population of the city and destroyed its fortifications,[a] in punishment for assisting Joscelin in this attempt. According to Thomas Asbridge, the women and children of Edessa were enslaved. He secured his hold on Antioch after crushing Raymond of Poitiers at the Battle of Inab in 1149, even presenting to the caliph, Raymond's severed head and arms.
Nur ad-Din sought to make alliances with his Muslim neighbours in northern Iraq and Syria in order to strengthen the Muslim front against their Crusader enemies. In 1147 he signed a bilateral treaty with Mu'in ad-Din Unur, governor of Damascus. As part of this agreement, he also married Mu'in ad-Din's daughter Ismat ad-Din Khatun. Together Mu'in ad-Din and Nur ad-Din besieged the cities of Bosra (see Battle of Bosra) and Salkhad, which had been captured by a rebellious vassal of Mu'in ad-Din named Altuntash, but Mu'in ad-Din was always suspicious of Nur ad-Din's intentions and did not want to offend his former crusader allies in Jerusalem, who had helped defend Damascus against Zengi. To reassure Mu'in ad-Din, Nur ad-Din curtailed his stay in Damascus and turned instead towards the Principality of Antioch, where he was able to seize Artah, Kafar Latha, Basarfut, and Balat.
In 1148, the Second Crusade arrived in Syria, led by Louis VII of France and Conrad III of Germany. Nur ad-Din's victories and the Crusader's losses in Asia Minor however had made the recovery of Edessa – their original goal – practically impossible. Given that Aleppo was too far off from Jerusalem for an attack and Damascus, recently allied with the Kingdom of Jerusalem against Zengi, had entered into an alliance with Nur ad-Din, the Crusaders decided to attack Damascus, the conquest of which would preclude a combination of Jerusalem's enemies. Mu'in ad-Din reluctantly called for help from Nur ad-Din, but the crusader siege collapsed after only four days.
Nur ad-Din took advantage of the failure of the Crusade to prepare another attack against Antioch. In 1149, he launched an offensive against the territories dominated by the castle of Harim, situated on the eastern bank of the Orontes, after which he besieged the castle of Inab. The Prince of Antioch, Raymond of Poitiers, quickly came to the aid of the besieged citadel. The Muslim army destroyed the Crusader army at the Battle of Inab, during which Raymond was killed. Raymond's head was sent to Nur ad-Din, who sent it along to the Caliph in Baghdad. Nur ad-Din marched all the way to the coast and expressed his dominance of Syria by symbolically bathing in the Mediterranean. He did not, however, attack Antioch itself; he was content with capturing all Antiochene territory east of the Orontes and leaving a rump state around the city, which in any case soon fell under the suzerainty of the Byzantine Empire. In 1150, he defeated Joscelin II for a final time, after allying with the Seljuk Sultan of Rüm, Mas'ud (whose daughter he also married). Joscelin was blinded and died in his prison in Aleppo in 1159. In the Battle of Aintab, Nur ad-Din tried but failed to prevent King Baldwin III of Jerusalem's evacuation of the Latin Christian residents of Turbessel. In 1152 Nur ad-Din captured and burned Tortosa, briefly occupying the town.