What were the major reasons for the decline of both the Umayyad and Abbasid Caliphates? What role ...

ANSWER:
The Umayyads were predominantly a political rather than a religious entity, focusing on an ethnically Arab realm rather than a Muslim one. They initially ruled from Damascus and had the backing of an Arab army, used Arabic as the primary language, and were slow to initiate placement of Muslim officials upon taking power. In fact, converts to Islam were a majority, compared to a small minority of Arabs holding power, and thus were disgruntled about a lack of equal status. Rebellions began among the Shi'ites and Kharijites, who saw the Umayyads as too secular and corrupt. The Abbasid Caliphate, by comparison, grew into a large, cosmopolitan community focused on Islam. It was a multicultural court that emphasized literature and culture and benefited from trade with China and other regions, but Baghdad culture moved only slowly into the more far-flung regions. In comparison to the Umayyad, the Abbasid Caliphate was focused on religion and commonality among a very heterogeneous population (umma) and was less concerned about ethnicity; but it was this heterogeneity that led to fragmentation and decentralization in favor of localism, albeit Muslim. Thus the Fatimid, Samanid, and al-Andalus Umayyads gained significant strength and power as the Abbasids declined.