Expansion and Consolidation of Islam in Iran to the End of Qajar Period

Dozy says in his excellent work on Islam, “During the first half of the seventh
century, everything followed its accustomed course in the Byzantine as in the
Persian empire. These two cities continued always to dispute the possession of
western Asia; there were, to all outward appearance, flourishing; the taxes which
poured into the treasuries of their kings reached considerable sums, and the
magnificence, as well as in the luxury of their capitals had become proverbial. But
all this was in appearance, for a secret disease consumed both empires; they were
burdened by a crushing despotism; on either hand the history of the dynasties
formed a concatenation of horrors, that of state a series of persecutions born of
dissentions in religious matters.