Persians/History

By the end of the Sassanian dynasty, the Persians and the Romans had been involved in countless wars which sapped all semblance of stability throughout the Levant. War exhaustion and political instability had eroded the ability of the Sassanian court to effective impose its will, so once the first warriors of the Rashidun caliphate arrived, the Sassanian empire simply collapsed before the Muslim invaders.

Even so, Arab control of Iran proved to be tenuous. Insurrections eventually doomed the Umayyad empire (although Umayyad rule of Spain would continue until the close of the 10th century), and soon a new leader, Abbas ibn Abd al-Muttalib, a relative of the Prophet, was appointed as caliph, forming a new dynasty called the Abbasid caliphate.

Fall of the Old Ways
Contrary to popular(ly misguided) preconceptions in contemporary culture, the process of Islamisation of Iran was not an overnight process, nor did it involve mass slaughter as some of Islam's biggest detractors might argue. Rather, it was a process that took at least several centuries, and while it certainly meant the end of Iran's indigenous religious beliefs, it did not spell the end of Iranian culture or even the end of Zoroastrianism itself.