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 of 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 Rum threatened Edessa and other cities.