Byzantine-Empire.com

This is a pie chart showing the distribution of the population of the Byzantine Empire in 560s AD at the end of the Justinian era.

As one can see, Anatolia had the greatest percentage of citizens in the empire.

Syria and Egypt were the next most populus regions of the empire.

These were the regions of the empire conquered by ShahShah Khosrow II in his attempt to reestablish the old borders of the Achaemenid Empire.

By the time you get to the Macedonian Dynasty in the late 9th Century, only the Balkans, Greece and Anatolia would remain.

The Byzantine Empire became much more Greek and Balkans oriented

In many ways, after the Muslim conquests, the empire became truly Greek and less diverse than it originally had been.

The empire was less diverse but it was coherent and less prone to civil strife in comparison to the earlier eras of the empire.