The Evolution of Islam in the Middle East

Historians often talk about Europe on the one hand and then the Islamic world at this time. Was there a certain amount of coherence between Islamic states and empires or were they all fairly distinct entities that maybe are not that helpfully termed as one big Islamic world? The expansion of Islam in this period is like wildfire. It's quite extraordinary in contrast to the development of any other religious belief that's tied to imperial power, much more dynamic certainly than Christianity is in this period.