### Instruction: When did Iranians convert to Islam?
### Input: The Islamization of Iran occurred as a result of the Muslim conquest of Persia in 633–654. It was a long process by which Islam, though initially rejected, eventually spread among the population on the Iranian Plateau. Iranian peoples have maintained certain pre-Islamic traditions, including their language and culture, and adapted them with Islamic codes. These two customs and traditions merged as the "Iranian Islamic" identity.
### Response: Unlike the popular opinion that Arabs converted Iranians to Islam after defeating the Sasanian Empire, Iranians continued to practice their native religions for many centuries. The conversion to Islam was a slow process which was aided by differentiated tax systems for Muslims and non-muslims.