This is a chapter from De Lacy O'Leary's 1922 scholarly history of Arabic intellectual culture, written in the tradition of Western Orientalist historiography. The excerpt traces the political and religious grievances that drove non-Arab converts (mawali) to revolt against Umayyad rule, arguing that the core tension was not religious persecution or racial animosity but a class-based resentment combined with Persian cultural expectations of divine kingship. O'Leary contends that Persians who converted to Islam found the Umayyad conception of the Khalif as a merely elected tribal chieftain deeply unsatisfying, since their own traditions demanded a semi-divine ruler embodying an incarnate spirit — a worldview he traces from Sasanid "bagh" theology through the Shi'a doctrine of the Imamate. He gives a detailed account of Shi'a sectarian genealogy, explaining how the various factions (Kaysanites, Twelvers, Zaydi rationalists, the Isma'ili Batinites) all share the distinctively Persian idea of the "concealed" Imam who will return. A notably distinctive claim is that the Shi'a movement is fundamentally foreign to Islam proper — a vehicle for Persian religious instincts and Hellenistic philosophical tendencies that found cover under Islamic legitimism — and that this same heterodox current was the channel through which Greek learning entered the Arabic intellectual tradition.