The problem of the Abbasids; the House of Barmak; the crumbling of the empire; the Prætorians of Baghdad; the Buwayhids; the situation of the Khalifa under them; the Saljuqs; the possibilities of development under them; the Mongols and the Abbasid end; the Egyptian Abbasids; the Ottoman Sultans, their heirs; theory of the Khalifate; the modern situation; the signs of sovereignty for Muslims; five grounds of the claim of the Ottoman Sultan; the consequences for the Sultan; other Muslim constitutions; the Shi‘ites; the Ibadites; the Wahhabites; the Brotherhood of as-Sanusi. [Sidenote: CRUMBLING OF THE EMPIRE] We must now return to the Abbasids, whose empire we left crumbling away. It was a shrewd stroke of policy on the part of its founder to put the new capital, Baghdad, on the Tigris, right between Persia, Syria and Arabia. For the only hope of permanence to the empire lay in welding these into a unity. For a short time, in the hands of the first vigorous rulers, and, especially, during fifty years of guidance by the House of Barmak—Persians who flung in their lot with the Abbasids and were their stay till the madness of Harun ar-Rashid cast them down—this seemed to be succeeding; but, just as the empire of Charlemagne melted under his sons, so did the empire of al-Mansur and al-Ma’mun. The Bedawi tribes fell back into the desert and to the free chaos of the old pre-Islamic life. As the great philosophical historian, Ibn Khaldun, has remarked, the Arabs by their nature are incapable of founding an empire except when united by religious enthusiasm, and are of all peoples least capable of governing an empire when founded. After the first Abbasids, it is a fatal error to view the Muslim dynasties as Arab or to speak of the Muslim civilization as Arabian. The conquered peoples overcame their conquerors. Persian nationalism reasserted itself and in native independent dynasties flung off the Arab yoke. These dynasties were mostly Shi‘ite; Shi‘ism, in great part, is the revolt of the Aryan against Semitic monotheism. The process in all this was gradual but certain. Governors of provinces revolted and became semi-independent. Sometimes they acknowledged a shadowy sovereignty of the Khalifa, by having his name on their coins and in the Friday prayers; sometimes they did not. At other times they were, or claimed to be, Alids, and when Alids revolted, they revolted absolutely. With them, it was a question of conscience. At last, not even in his own City of Peace or in his own palace was the Khalifa master. As in Rome, so in Baghdad, a body-guard of mercenaries assumed control and their leader was _de facto_ ruler. Later, from A.H. 320 to 447 (A.D. 932-1055), the Sunnite Khalifa found himself the ward and puppet of the Shi‘ite Buwayhids. Baghdad itself they held from 334. But still, a curious spiritual value—we cannot call it authority—was left to the shadowy successors of Muhammad.