As I was eating my sandwich a thought occurred to me, prior to the Islamic conquest, Mesopotamia was a mix of heretics and infidels of varying degree to the Rhomans. Regardless of how such a thing would occur, how would these people have been treated as part of the empire should Mesopotamia had been annexed from the Sassanids.
If you were wondering, I'm focused more around early Justinian/pre-eternal peace treaty annexation than anything later.
If you were wondering, I'm focused more around early Justinian/pre-eternal peace treaty annexation than anything later.