The empire founded by the Caliph ‘Umar and administered by the Umayyads was essentially, as the reader will have gathered, a military organisation for the benefit of the paramount race. In theory, no doubt, all Moslems were equal, but in fact the Arabs alone ruled--a privilege which national pride conspired with personal interest to maintain. We have seen how the Persian Moslems asserted their right to a share in the government. The Revolution which enthroned the ‘Abbásids marks the beginning of a Moslem, as opposed to an Arabian, Empire. The new dynasty, owing its rise to the people of Persia, and especially of Khurásán, could exist only by establishing a balance of power between Persians and Arabs. That this policy was not permanently successful will surprise no one who considers the widely diverse characteristics of the two races, but for the next fifty years the rivals worked together in tolerable harmony, thanks to the genius of Manṣúr and the conciliatory influence of the Barmecides, by whose overthrow the alliance was virtually dissolved. In the ensuing civil war between the sons of Hárún al-Rashíd the Arabs fought on the side of Amín while the Persians supported Ma’mún, and henceforth each race began to follow an independent path. The process of separation, however, was very gradual, and long before it was completed the religious and intellectual life of both nationalities had become inseparably mingled in the full stream of Moslem civilisation. [Sidenote: The choice of a new capital.] [Sidenote: Foundation of Baghdád.]