The typical outlook about the Muslim attacks against Iran is the view
stating that Iranians due to the oppressive and disproportionate scheme
ruled over Sassanids society, acclaimed the Muslims. According to some
contemporary researchers, if Islam had not have entered Iran, Christianity
would have been able to spread in Iran. However, Irans history shows that
Iranians were faithful to Zoroastrianism up to the end of the fifth century
(based on Hijrah of the Prophet).