The Crusader invasions of Egypt (1163–1169) were a series of campaigns undertaken by the Kingdom of Jerusalem to strengthen its position in the Levant by taking advantage of the weakness of Fatimid Egypt. The war began as part of a succession crisis in the Fatimid Caliphate, which began to crumble under the pressure of Muslim Syria ruled by the Zengid dynasty and the Christian Crusader states. While one side called for help from the emir of Syria, Nur ad-Din Zangi, the other called for Crusader assistance. As the war progressed, however, it became a war of conquest. A number of Syrian campaigns into Egypt were stopped short of total victory by the aggressive campaigning of Amalric I of Jerusalem. Even so, the Crusaders generally speaking did not have things go their way, despite several sackings. A combined Byzantine-Crusader siege of Damietta failed in 1169, the same year that Saladin took power in Egypt as vizier. In 1171, Saladin became sultan of Egypt and the crusaders thereafter turned their attention to the defence of their kingdom.