1. Firstly the difference was constitutional. The Orthodox Caliphate was an elective republican state. The Umayyad Caliphate, on the contrary, became a hereditary monarch. 2. Secondly, the Orthodox Caliphate was a religio-political Commonwealth. But Umayyad Caliphate was a secular state, such as could exist in the ancient times. Many of the Umayyad caliphs were not particularly loyal to the Political implication and private lives. 3. Thirdly, though Arabian in origin and personnel, Orthodox Caliphate was not Arabistic in policy and purpose. The Umayyad Caliphate, on the contrary, was as Wellhausen says an Arab Kingdom, that is, a government of the Arabs by the Arabs and for the Arabs. The Arabs formed its ruling class and monopolised its political power and economic privileges. The non-Arabs, even though they be Muslims were excluded from a Share in its government and its political, economic and social benefits. In other words while the Arabs were its f...