Islam in Iran
The Arab conquest of Iran, which culminated in the fall of the Sasanian Empire to the nascent Rashidun Caliphate, brought about a monumental change in Iranian society by purging Zoroastrianism, which had been Iran’s official and majority religion since the time of the Achaemenid Empire. Since the Rashidun invasion, Islam has consistently held the status of Iran's official religion except for a short period in the 13th century, when the Mongol invasions and conquests destroyed the Abbasid Caliphate and smaller Islamic realms before resulting in the establishment of the Ilkhanate. The process by which Iranian society became integrated into the Muslim world took place over many centuries, with nobility and city-dwellers being among the first to convert, in spite of notable periods of resistance, while the peasantry and the dehqans took longer to do so. Around the 10th century, most Persians had become Muslims.
Between the 7th century and the 15th century, Sunni Islam was the dominant sect in Iran, and Iranian academics of this period contributed greatly to the Islamic Golden Age. In the 16th century, the newly enthroned Safavid dynasty initiated a massive campaign to install Shia Islam as Iran's official sect, aggressively proselytizing the faith and forcibly converting the Iranian populace. The Safavids' actions triggered tensions with the neighbouring Sunni-majority Ottoman Empire, in part due to the flight of non-Shia refugees from Iran. It is estimated that by the mid-17th century, Iran had become a Shia-majority nation. Over the following centuries, with the state-fostered rise of an Iran-based Shia clergy, a synthesis was formed between Iranian culture and Shia Islam that marked each indelibly with the tincture of the other. Later, under the Pahlavi dynasty, Islamic influence on Iranian society was rolled back in order to assert a new Iranian national identity—one that focused on pre-Islamic Iran by shedding more light on Zoroastrian tradition and other aspects of ancient Iranian society, particularly during the Achaemenid era. However, in 1979, the Islamic Revolution brought about yet another monumental change by ending the historic Iranian monarchy and replacing it with an Islamic republic.
Modern estimates of religious adherence
According to an October 2024 update to Britannica.com by scholars at the Universities of Cambridge and Utah, as of the date of their source data, Muslims accounted for 99.6% of the total population of Iran and comparable older numbers and somewhat discrepant more recent numbers, at CIA.gov—with the "vast majority... of the Ithnā ʿAsharī, or Twelver, Shiʿi branch".The Iranian government's 2016 census purportedly presents 99% of the Iranian population as Muslim, and 80% of this figure is composed of Twelver Shias. Approximately 7% of Iranians are Sunnis. According to scholars at the Universities of Cambridge and Utah, the country's "Kurds and Turkmen are predominantly Sunni Muslims", with Iran's Arab population being split between "Sunni and Shiʿi". Other sources note that this smaller percentage comprises the country's ethnic minorities, the Kurds, Turkmens, and Arabs, as well as Achomi Persians, Khorasani Persians, and Baloch.
According to the 2020 Wave 7 World Values Survey, 96% of Iranians identify as Muslims. However, a report by the Group for Analyzing and Measuring Attitudes in Iran in the same year showed a sharp decline in religiosity in the country, as only 40% of Iranian respondents identified as Muslims. Subsequent GAMAAN surveys in 2022 showed that, 38% to 56% identified as Shia Muslims, 5% identified as Sunni Muslims, and roughly a quarter of were susceptible to a form of deism—that is, belief in God without identifying as religious. In all GAMAAN surveys, 7% to 10% of Iranian respondents identified as atheists. The survey is however questionable as it used self-selecting participants, reached through social media and chain referrals.
History
Arab conquest of Iran
Muslims conquered Iran in the time of Umar and conquered it after several great battles. Yazdegerd III fled from one district to another Merv in 651. By 674, Muslims had conquered Greater Khorasan.As Bernard Lewis has quoted
"These events have been variously seen in Iran: by some as a blessing, the advent of the true faith, the end of the age of ignorance and heathenism; by others as a humiliating national defeat, the conquest and subjugation of the country by foreign invaders. Both perceptions are of course valid, depending on one's angle of vision."
Under Umar and his immediate successors, the Arab conquerors attempted to maintain their political and cultural cohesion despite the attractions of the civilizations they had conquered. The Arabs were to settle in the garrison towns rather than on scattered estates. The new non-Muslim subjects, or dhimmi, were to pay a special tax, the jizya or poll tax, which was calculated per individual at varying rates for able bodied men of military age.
Iranians were among the very earliest converts to Islam, and their conversion in significant numbers began as soon as the Arab armies reached and overran the Persian plateau. Despite some resistance from elements of the Zoroastrian clergy and other ancient religions, the anti-Islamic policies of later conquerors like the Il-khanids, the impact of the Christian and secular West in modern times, and the attraction of new religious movements like Babism and the Baháʼí Faith, the vast majority of Iranians became and have remained Muslims. Today perhaps 98 percent of ethnic Iranians, including the population of Persia, are at least nominal Muslims. For such a fundamental, pervasive, and enduring cultural transformation, the phenomenon of Iranian conversions to Islam has received remarkably little scholarly attention.
Recent research has established a general chronological framework for the process of conversion of Iranians to Islam. From a study of the probable dates of individual conversions based on genealogies in biographical dictionaries, Richard Bulliet has suggested that there was gradual and limited conversion of Persians down to the end of the Umayyad period, followed by a rapid increase in the number of conversions after the ʿAbbasid revolution, so that by the time when regional dynasties had been established in the east 80 percent or more of Iranians had become Muslims. The data on which Bulliet's study was based limited the validity of this paradigm to generalizations about full, formal conversions in an urban environment. The situation in rural areas and individual regions may have been quite different, but the overall pattern is consistent with what can be deduced from traditional historical sources. Although in some areas, for example, Shiraz at the time of Moqaddasi's visit in about 375/985, there may still have been strong non-Muslim elements, it is reasonable to suppose that the Persian milieu as a whole became predominantly Islamic within the period of time suggested by Bulliet's research.
Islamization of Iran
Following the Abbasid revolution of 749–51, in which Iranian converts played a major role, the Caliphate's center of gravity moved to Mesopotamia and underwent significant Iranian influences. Accordingly, the Muslim population of Iran rose from approx. 40% in the mid 9th century to close to 100% by the end of the 11th century. Islam was readily accepted by Zoroastrians who were employed in industrial and artisan positions because, according to Zoroastrian dogma, such occupations that involved defiling fire made them impure. Moreover, Muslim missionaries did not encounter difficulty in explaining Islamic tenets to Zoroastrians, as there were many similarities between the faiths. According to Thomas Walker Arnold, for the Persian, he would meet Ahura Mazda and Ahriman under the names of Allah and Iblis. Muslim leaders in their effort to win converts encouraged attendance at Muslim prayer, and allowed the Quran to be recited in Persian instead of Arabic so that it would be intelligible to all. The first complete translation of the Qur'an into Persian occurred during the reign of Samanids in the 9th century. Seyyed Hossein Nasr suggests that the rapid increase in conversion was aided by the Persian nationality of the rulers.According to Bernard Lewis:
"Iran was indeed Islamized, but it was not Arabized. Persians remained Persians. And after an interval of silence, Iran reemerged as a separate, different and distinctive element within Islam, eventually adding a new element even to Islam itself. Culturally, politically, and most remarkable of all even religiously, the Iranian contribution to this new Islamic civilization is of immense importance. The work of Iranians can be seen in every field of cultural endeavor, including Arabic poetry, to which poets of Iranian origin composing their poems in Arabic made a very significant contribution. In a sense, Iranian Islam is a second advent of Islam itself, a new Islam sometimes referred to as Islam-i Ajam. It was this Persian Islam, rather than the original Arab Islam, that was brought to new areas and new peoples: to the Turks, first in Central Asia and then in the Middle East in the country which came to be called Turkey, and India. The Ottoman Turks brought a form of Iranian civilization to the walls of Vienna..."
Iranian influence on Muslim civilization
The Islamization of Iran was to yield deep transformations within the cultural, scientific, and political structure of Iran's society: The blossoming of Persian literature, philosophy, medicine and art became major elements of the newly forming Muslim civilization. Inheriting a heritage of thousands of years of civilization, and being at the "crossroads of the major cultural highways", contributed to Persia emerging as what culminated into the "Islamic Golden Age". During this period, hundreds of scholars and scientists vastly contributed to technology, science and medicine, later influencing the rise of European science during the Renaissance.The most important scholars of almost all of the Islamic sects and schools of thought were Persian or live in Iran including most notable and reliable Hadith collectors of Shia and Sunni like Shaikh Saduq, Shaikh Kulainy, Imam Bukhari, Imam Muslim and Hakim al-Nishaburi, the greatest theologians of Shia and Sunni like Shaykh Tusi, Imam Ghazali, Imam Fakhr al-Razi and Al-Zamakhshari, the greatest physicians, astronomers, logicians, mathematicians, metaphysicians, philosophers and scientists like Al-Farabi, Avicenna, and Nasīr al-Dīn al-Tūsī, the greatest Shaykh of Sufism like Rumi, Abdul-Qadir Gilani.
Ibn Khaldun narrates in his Muqaddimah:
It is a remarkable fact that, with few exceptions, most Muslim scholars… in the intellectual sciences have been non-Arabs, thus the founders of grammar were Sibawaih and after him, al-Farsi and Az-Zajjaj. All of them were of Persian descent... they invented rules of grammar. Great jurists were Persians. Only the Persians engaged in the task of preserving knowledge and writing systematic scholarly works. Thus the truth of the statement of the prophet becomes apparent, "If learning were suspended in the highest parts of heaven the Persians would attain it"… The intellectual sciences were also the preserve of the Persians, left alone by the Arabs, who did not cultivate them… as was the case with all crafts… This situation continued in the cities as long as the Persians and Persian countries, Iraq, Khorasan and Transoxiana, retained their sedentary culture.