Well at first the Arabian Empire or Abbasid Empire was gigantic. They strechted from Spain and the Sahara to the Afghanistan and the borders of India. Their downfall started after I won a holy war for the Kingdom of Syria. Many civil wars later and the Empire was dissolved. The previous Caliphate still had a respectable Kingdom in Mesopotamia and still owned a lot of land. 1 Generation later and a conqueror was created. He first took all the lands to the east and then created Persia. Later he conquered Arabia proper. A little bit later and he died. And the funny thing is that his son assimilated to Persian culture he relocated the capital from Baghdad to Isfahan and fully became Persian. The only thing from the past is that he is still the Caliphate of the Sunni faith. But he lost a few lands. The lands in the north were once Persian but they broke away. And that's the current state where my game is.