The Muslim conquest of Persia, also known as the Arab conquest of Iran,^[29] occurred between 632 and 654 CE, leading to the fall of the Sasanian Empire and the decline of Zoroastrianism. This period coincided with significant political, social, economic, and military turmoil in Persia. The once powerful Sasanian Empire was weakened by prolonged warfare against the Byzantine Empire and internal political instability, particularly following Shah Khosrow II's execution in 628 and the subsequent enthronement of ten different claimants in four years.

The Arab Muslims, under the Rashidun Caliphate, initially invaded Sasanian territory in 633, with Khalid ibn al-Walid attacking the key province of Asōristān (modern Iraq). Despite initial setbacks and Sasanian counterattacks, the Muslims achieved a decisive victory at the Battle of al-Qadisiyyah in 636 under Sa'd ibn Abi Waqqas, leading to the loss of Sasanian control west of Iran. The Zagros Mountains served as a border between the Rashidun Caliphate and the Sasanian Empire until 642, when Caliph Umar ibn al-Khattab ordered a full-scale invasion, resulting in the complete conquest of the Sasanian Empire by 651.^[30]

Despite the rapid conquest, Iranian resistance to the Arab invaders was significant. Many urban centers, except in regions like Tabaristan and Transoxiana, fell to Arab control by 651. Numerous cities rebelled, killing Arab governors or attacking garrisons, but Arab reinforcements eventually suppressed these uprisings, establishing Islamic control. The Islamization of Iran was a gradual process, incentivized over centuries. Despite violent resistance in some areas, the Persian language and Iranian culture persisted, with Islam becoming the dominant religion by the late Middle Ages.^[31]