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 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. 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, in punishment for assisting Joscelin in this attempt. According to Thomas Asbridge, the women and children of Edessa were enslaved.