The Osmanlis, whose nomadic forefathers had fled before the face of the Mongols out of Central Asia, took the heritage which had slipped from the Mongols' grasp, and gathered all threads of authority in Western Asia into their hands. The most valuable spoil of their Asiatic conquests was the Caliphate. Hulaku, the sacker of Bagdad, had put the Caliph Mustasim to death, and the remnant of the Abbasids had kept up a shadowy succession at Cairo, under the protection of the Sultan of Egypt. Selim the Osmanli, when he entered Cairo as a conqueror in 1517, caused the contemporary Abbasid to cede his title, for what it was worth, to him and his successors. It was a doubtful title, scorned by all Shias and regarded coldly by many Sunni rulers who were unwilling to recognise a spiritual superior in their most formidable temporal rival. But such as it was, it strengthened the Osmanli's hold on his dominions. Caliph of Islam, victorious guardian of the Moslem marches, and heir by conquest of imperial Rûm, the Osmanli Sultan held his Asiatic provinces with ease; but the best security for his tenure was the misery to which they were reduced. Commerce and cultivation ebbed, population dwindled, and nomads still drifted in upon what once had been settled lands. The Ottoman Government, desiring a barrier against Persia, encouraged the Kurds to spread themselves over Armenia; it welcomed less the Shammar and Anazeh Arabs, who broke over the Euphrates about the year 1700 and turned the last fields of Northern Mesopotamia to desolation; but it was too impotent or indifferent to turn them out. Western Asia lay fallow under the Ottoman cannon-wheels. There have been fallow periods before in the slow rhythm of its life--under the Persians, for instance, who overran all lands and peoples of the East in the sixth century B.C., overshadowed the Greeks for a moment, as the Osmanlis overshadowed Europe, halted, too massive for offence but seemingly unassailable, and then collapsed pitifully before the probing spears of Alexander.