It was the lust of conquest even more than missionary zeal that caused the Arabs to invade Syria and Persia and to settle on foreign soil, where they lived as soldiers at the expense of the native population whom they inevitably regarded as an inferior race. If the latter thought to win respect by embracing the religion of their conquerors, they found themselves sadly mistaken. The new converts were attached as clients (_Mawálí_, sing. _Mawlá_) to an Arab tribe: they could not become Moslems on any other footing. Far from obtaining the equal rights which they coveted, and which, according to the principles of Islam, they should have enjoyed, the _Mawálí_ were treated by their aristocratic patrons with contempt, and had to submit to every kind of social degradation, while instead of being exempted from the capitation-tax paid by non-Moslems, they still remained liable to the ever-increasing exactions of Government officials. And these 'Clients,' be it remembered, were not ignorant serfs, but men whose culture was acknowledged by the Arabs themselves--men who formed the backbone of the influential learned class and ardently prosecuted those studies, Divinity and Jurisprudence, which were then held in highest esteem. Here was a situation full of danger. Against Shí‘ites and Khárijites the Umayyads might claim with some show of reason to represent the cause of law and order, if not of Islam; against the bitter cry of the oppressed _Mawálí_ they had no argument save the sword. [Sidenote: Presages of the Revolution.] We have referred above to the universal belief of Moslems in a Messiah and to the extraordinary influence of that belief on their religious and political history. No wonder that in this unhappy epoch thousands of people, utterly disgusted with life as they found it, should have indulged in visions of 'a good time coming,' which was expected to coincide with the end of the first century of the Hijra. Mysterious predictions, dark sayings attributed to Muḥammad himself, prophecies of war and deliverance floated to and fro. Men pored over apocryphal books, and asked whether the days of confusion and slaughter (_al-harj_), which, it is known, shall herald the appearance of the Mahdí, had not actually begun. The final struggle was short and decisive. When it closed, the Umayyads and with them the dominion of the Arabs had passed away. Alike in politics and literature, the Persian race asserted its supremacy. We shall now relate the story of this Revolution as briefly as possible, leaving the results to be considered in a new chapter. [Sidenote: The ‘Abbásids.] [Sidenote: ‘Abbásid propaganda in Khurásán.]