Islam
The Mamluks
Many of the Ayyubid rulers were using slaves as soldiers, a practice that became widespread in the 12th century. The Sultan and various emirs recruited boys from southern Russia—the Kipchak Turks of the lower Volga River was a favorite source. The boys were slaves, but they were brought up in the Faith and their lives were devoted to military instruction. By the time they were of fighting age, they were well-trained and were utterly devoted to one another and to their commanders.
This system worked well so long as the leaders were strong, but the Ayyubid dynasty degenerated quickly after the death of al-Kamil, especially at Cairo. When the Seventh Crusade came along, it precipitated a rebellion, led by the Mamluk chieftain Baibars. He killed the Sultan and the Caliph, and ensured that the Caliph's place was taken by a small boy who would not question Baibars' position. That revolt is recounted elsewhere.
The revolt ended the Ayyubid sultanate at Cairo, founded by Saladin. In Baibars, Islam found a new champion who proceeded vigorously against the Christians. In many other ways, however, the Mamluk revolution changed little in Egypt. The Mamluk Sultans inherited most of the Ayyubid political program, fiscal policies, and so on. They continued to recruit soldier-slaves and these continued to form the foundation of the army. The Mamluks produced a series of strong leaders in the 13th century who were responsible both for driving the Franj out of Syria and Palestine, and for turning back the Mongol advance that was devastating the lands of Islam.