There are many maps and animations circulating on the internet which purport to show the historical “spread of Islam” under the leadership of Prophet Muhammad (ṣ, d. 632 CE) and in subsequent generations of Muslims. But do these maps really show the spread of Islam or just the conquests of the Arab-Muslim armies? There is an important difference between these two interpretations, because the first implies that large non-Muslim populations in the conquered regions must have been forced to convert to Islam, while the second implies that the Muslim conquests weren’t necessarily accompanied by mass forced conversions to Islam.
The historical evidence we have lends its weight to the second interpretation. The conquests began in around 632 CE, immediately after Prophet Muhammad (ṣ) passed away. The early Muslims then began to dismantle the Byzantine (Roman) and Sassanid (Persian) empires. A century later (in 732) the Islamic empire, now ruled by the Umayyad dynasty, extended from Spain in the west to India in the east; at the time, it was the largest empire in world history.
But does this mean that all the non-Muslims in that vast territory – Christians, Jews, Zoroastrians, Buddhists, Hindus, and others – had been forced to convert to Islam? The simple historical fact is that no, they were not, and this is something that leading Muslim and non-Muslim historians agree on. This article aims to present some of their positions and arguments to provide food for thought to anyone who is genuinely interested in historical facts and not simply trying to superimpose his/her anti-Islam bigotry onto the past.
Generally, forced conversion is explicitly forbidden in Islam. In the Qur’ān, Muslims are reminded that “[t]here shall be no compulsion in [acceptance of] the religion [of Islam]” (2:256). Classical commentators on the Qur’ān, such as the famous Ismā‘īl ibn Kathīr (d. 1373), and more recent ones such as Sayyid Qutb (d. 1966) and Mawdūdī (d. 1979) are in agreement that this passage forbids any form of coercing non-Muslims into embracing Islam.  However, many (if not most) of the people who express curiosity about whether Islam spread “by the sword” are interested in whether this is a historical reality; and therefore I won’t delve any further into the Qur’anic prohibition on forced conversion.
With that in mind, we can begin to explore what historians say about forced conversions to Islam in history. In general, they say that these forced conversions did occur, but rarely. Professor Ira M. Lapidus, for example, writes that “[t]he question of why people convert to Islam has always generated intense feeling. Earlier generations of European scholars believed that conversions to Islam were made at the point of the sword and that conquered peoples were given the choice of conversion or death. It is now apparent that conversion by force, while not unknown in Muslim countries, was, in fact, rare. Muslim conquerors ordinarily wished to dominate rather than convert, and most conversions to Islam were voluntary.” 
Similarly, the late Marshall Hodgson wrote in his ground-breaking work The Venture of Islam that “[t]here was no attempt [by the Muslims] at converting the peoples of the [conquered] imperial territories, who practically all adhered to some form of confessional religion already… In the chiefly non-Arab agricultural lands, the object was not conversion but rule… The superiority of Islam as religion, and therefore in providing for social order, would justify Muslim rule; would justify the simple, fair-dealing Muslims in replacing the privileged and oppressive representatives of the older, corrupted allegiances…” 
It should be noted that both Lapidus and Hodgson are considered leading authorities in the field of Islamic history. But while they offer the general statements quoted above, we can turn to the work of Hugh Kennedy, another prominent historian, for specific examples. Kennedy quotes the treaty signed between Sophronius, the patriarch of recently-conquered Jerusalem, and the second Muslim caliph, ‘Umar ibn al-Khattāb (d. 644):
“This is the assurance of safety [amān] which the servant of God, ‘Umar, the Commander of the Faithful, has given to the people of Jerusalem. He has given them an assurance of safety for themselves, for their property, their churches, their crosses, the sick and healthy of the city and for all the rituals which belong to their religion. Their churches will not be inhabited by the Muslims and will not be destroyed. Neither they, nor the land on which they stand, nor their cross, not their property will be damaged. They will not be forcibly converted…” 
‘Umar is generally regarded as having been one of the more strict caliphs, and Jerusalem was very symbolically important city for the Muslims; therefore, we have reason to believe that if the Muslims had been forcibly converting non-Muslims as they conquered their lands, Jerusalem would not have been the exception.
Decades after ‘Umar’s treaty with Sophronius, the Muslim leader ‘Abd al-‘Azīz ibn Mūsa ibn Nusayr signed a similar treaty with a Visigothic noble (of southeastern Spain) named Theodemir in 713. One of the terms of the treaty was that “they [i.e. Theodemir’s followers] will not be coerced in matters of religion, their churches will not be burned, nor will their sacred objects be taken from them…” 
Of course, such agreements did come at a price for the conquered non-Muslims, but that price did not include their religious beliefs. They were obliged to pay the jizya, an annual tax which guaranteed the safety of their lives, property, and freedom of religion, exempted them from military service, and often left their pre-Islamic systems of administration and justice intact. The amount of the jizya was flexible, though it had to be kept affordable for those expected to pay it, namely, adult non-Muslim men who were able to earn a living. Children under the age of puberty, women, the elderly, and the physically and/or mentally impaired were all exempt from paying the jizya. 
It’s important to mention these details about the jizya because it is often described as an underhanded way of pressuring non-Muslims into converting to Islam. However, anyone who is familiar with world history can tell that considering the conditions of the jizya, it was hardly a burden at all compared to what other imperial systems (including many modern ones) demanded from the people they conquered. It is also important to keep in mind Muslims also had to pay a comparable annual tax, the zakāt, so embracing Islam was not necessarily a way out of the jizya that non-Muslims could be forced to take.
It has even been argued that, far from forcing disbelievers from converting to Islam, many Muslim rulers actually preferred to rule over non-Muslims and collect the jizya from them. This is because the zakāt collections were often redistributed locally in the provinces and could only be used in certain ways, but the jizya was sent to the central treasury in the capital, where the ruler could use it any way he wanted to. This certainly is not something that historians agree on, but it nonetheless shows that in reality forcing non-Muslims to embrace Islam was rarely, if ever, a priority for Muslims when they were in power.
And so it makes sense that it was the institution of the jizya, and not the dramatized “convert-or-die” choice that many people imagine was put to non-Muslims, which ensured that Islam remained a minority religion in the conquered territories for a long time after the conquest. Historians suggest different figures, but generally agree that “for at least two centuries the majority of the inhabitants of the Islamic empire were non-Muslims.” 
Other historians confirm that, in the regions conquered in the first century of the Muslim conquests (i.e. 632-732), Islam didn’t become a majority religion until 850-1050. Nearly all of Iran, for example, had been conquered by 705; however, the empirical research of Richard Bulliet has shown that it was only in the mid-9th century that the percentage of Muslims in Iran’s population reached 50%, and it took nearly another century after that for that figure to hit 75%.  Similarly, the region that makes up today’s Albania was gradually conquered by the Ottomans over the course of the 15th century, but conversion to Islam only really took off in the second half of the 17th century, nearly 200 years later.  As some historians have pointed out, “if forced conversion to Islam had been the impetus behind the conquests, they were a miserable failure.” 
Of course, there were some forced conversions in Islamic history. The Ottomans, for example, tried their hand at the forced conversion of Christians in the Balkans. This was done mostly through the devshirme system, in which one in every 40 young Christian boys from the Balkans were taken once a year and brought up as Muslims to serve in the Ottoman sultan’s bureaucracy and army. However, this never amounted to forced conversion on a mass scale and even today, Islam remains a minority religion in the region.
So, if there were virtually no forced conversions in Islamic history, what does an effort at forced conversion actually look like? Incidentally, Muslims have been the victims of some of one of the worst cases of forced conversion in history: the Reconquista (medieval Christian conquest of Spain). Muslims ruled most of Spain for nearly 800 years, by the end of which (in the late 15th century) they had lost power in most of the region. As the Christian monarchs, Ferdinand and Isabella, jumped on the opportunity to reconquer Spain in the name of Christianity, they gave the following options to the million (or so) Muslims and Jews who lived there: convert to Christianity, leave Spain, or die.
Many chose to death over giving up their faith and their homeland; many hundreds of thousands others were forcibly converted and were known as Moriscos (former Muslims) or Moranos (former Jews). Between 1492 and 1609, even those who had been forced to convert were expelled, virtually eliminating the Muslim and Jewish presence in Spain in just one century.  Many of the refugees resettled in the Muslim-ruled regions of Eastern Europe at the Ottomans’ invitation, where ― far from being forced to convert to Islam ― most of them reverted back to their original faiths.
If the meager forces of the Christian city-states could use forced conversion and expulsion to complete eliminate Muslims and Jews from Spain in just one century, then why haven’t Muslims, who for most of history have had far more power over the disbelievers they ruled over, been able to do the same? The answer, of course, is straightforward: Muslims were not forcibly converting non-Muslims to Islam.
Finally, it is interesting to take note the distribution of Muslims today. Islam remains the predominant religion in regions that were conquered by the early Muslims, but many of the states in this region continue to be home to significant non-Muslim (Christian, Jewish, and other) populations. However, even larger populations of Muslims are to be found in Southeast Asia (e.g. Indonesia), China, and West Africa (e.g. Nigeria), where Islam spread through traders, scholars, and mystics, and where there was no Muslim conquest at all!
Perhaps it is safe to consider the possibility, then, that the Qur’ānic directive that “[t]here shall be no compulsion in [acceptance of] the religion [of Islam]” is not just a command for Muslims to follow, but also a matter-of-fact statement that Islam doesn’t need any forced conversions or compulsion of any kind toward disbelievers to be successful among them. And as the historical evidence indicates, the overwhelming majority of Muslims throughout history have understood this.
 See, for example, Ismā‘īl ibn Kathīr, Tafsīr Ibn Kathīr (Vol. 2), New York, NY: Darussalam Publishers, 2003, p. 30; and Sayyid Qutb, In the Shade of the Qur’ān (Vol. 1), The Islamic Foundation, 2015, p. 348-353.
 Ira M. Lapidus, A History of Islamic Societies, New York, NY: Cambridge University Press, 2014, p. 271.
 Marshall G. S. Hodgson, The Venture of Islam, Volume 1: The Classical Age of Islam, Chicago, IL: The University of Chicago Press, p. 199.
 Hugh Kennedy, The Great Arab Conquests: How the Spread of Islam Changed the World We Live In. Philadelphia, PA: Da Capo Press, 2007, p. 91.
 Ibid., p. 315.
 For more details and a complete list of conditions, see: Cahen, Cl., İnalcık, Halil and Hardy, P., “Ḏj̲izya”, in: Encyclopaedia of Islam, Second Edition, Edited by: P. Bearman, Th. Bianquis, C.E. Bosworth, E. van Donzel, W.P. Heinrichs. http://dx.doi.org.ezproxy.library.yorku.ca/10.1163/1573-3912_islam_COM_0192 and https://islamqa.info/en/214074.
 William L. Cleveland and Martin Bunton, A History of the Modern Middle East (4th ed.), Westview Press, 2009, p. 14.
 Richard W. Bulliet, “Conversion to Islam and the Emergence of a Muslim Society in Iran,” in Nehemia Levtzion (Ed.), Conversion to Islam, New York, NY: Holmes & Meier Publishers, 1979, p. 36.
 Krstic, Tijana. Contested Conversions to Islam: Narratives of Religious Change in the Early Modern Ottoman Empire, Stanford, CA: Stanford University Press, 2011, p. 21.
 Richard C. Martin, “Conversion to Islam by Invitation,” in John Witte Jr. and Richard C. Martin (Eds.), Sharing the Book: Religious Perspectives on the Rights and Wrongs of Proselytism, Eugene, OR: Wipf and Stock Publishers, 2008, p. 103.
 H. Michael Tarver and Emily Slape (Eds.). The Spanish Empire: A Historical Encyclopedia, ABC-CLIO, 2016, p. 207.