Sennar apportioned tributary areas into tribal homelands each one termed a dar (pl., dur), where the mek granted the local population the right to use arable land. The diverse groups that inhabited each dar eventually regarded themselves as units of tribes. Movement from one dar to another entailed a change in tribal identification. (Tribal distinctions in these areas in modern Sudan can be traced to this period.) The mek appointed a chieftain (nazir; pl., nawazir) to govern each dar. Nawazir administered dur according to customary law, paid tribute to the mek, and collected taxes. The mek also derived income from crown lands set aside for his use in each dar. At the peak of its power in the mid-17th century, Sennar repulsed the northward advance of the Nilotic Shilluk people up the White Nile and compelled many of them to submit to Funj authority. After this victory, the mek Badi II Abu Duqn (1642–81) sought to centralize the government of the confederacy of Sennar. To implement this policy, Badi introduced a standing army of slave soldiers that would free Sennar from dependence on vassal sultans for military assistance, and would provide the mek with the means to enforce his will. The move alienated the dynasty from the Funj warrior aristocracy which deposed the reigning mek, and placed one of their own ranks on the throne of Sennar in 1718. The mid-18th century witnessed another brief period of expansion when the Funj turned back an Abyssinian invasion, defeated the Fur, and took control of much of Kurdufan. But the civil war, and the demands of defending the sultanate, had overextended the warrior society's resources and sapped its strength. Another reason for Sennar's decline may have been the growing influence of its hereditary viziers (chancellors), chiefs of a non-Funj tributary tribe who managed court affairs. In 1761, the vizier Muhammad Abu al Kaylak, who had led the Funj army in wars, carried out a palace coup, relegating the sultan to a figurehead role. Sennar's hold over its vassals diminished, and by the early 19th century, more remote areas ceased to recognize even the nominal authority of the mek. The Fur Darfur was the Fur homeland. Renowned as cavalrymen, Fur clans frequently allied with, or opposed their kin, the Kanuri of Borno, in modern Nigeria. After a period of disorder in the sixteenth century, during which the region was briefly subject to the