The just war against Islam
A clash between Christianity and Islam was inevitable. Not only because they got into each other's way, but also because they used different justifications for warfare.
We have already discussed the attitude of the Christian Church towards pagans and heretics. As announced, we are now going to discuss the attitude of the Church towards the people of the book: later the Jews, but first the Muslims.
Military clashes between Christians and Muslims came in three waves, which we will cover next:
The expansion of the Caliphates, between the 7th and 9th centuries.
The Crusades, between the 11th and 13th centuries.
The expansion of the Ottoman Empire, between the 11th and 17th centuries.
Islamic expansion irrevocably brought about military and religious conflicts with the Christian states. The Muslims, like the Christians, were monotheistic, but whether it concerned the same god, wasn’t very clear at the time. Muslims claimed to be descendants of the biblical Abraham, and Muslims consider the Torah a holy book and Jesus a prophet.
He has revealed to you ˹O Prophet˺ the Book in truth, confirming what came before it, as He revealed the Torah and the Gospel
— Qur'an, Sura 3 (Al-Imran), verse 3
In Islamic theology, a distinction is made between the people of the book and polytheists. Where Christians and Jews were respected and could count on a degree of toleration, that toleration was considerably less for polytheists.
After discussing the greatest military clashes between Christianity and Islam, we get to the heart of the matter: the differing views in Christianity and Islam about the justification of war. In Christianity there was still some reluctance about waging war. There had to be a justification for it: self-defence, specifically. There was no such restraint in Islam. Any effort to expand the Islamic rule of law was justified, perhaps even a duty.
The Expansion of the Caliphates
In the 7th century, a new monotheistic religion had emerged among the Arabs, Islam, which soon became a formidable rival of Christianity. I will describe the history of Islam in more detail in a separate series on toleration and Islam.
In the last three years before his death in 632, the Arab Muhammad succeeded in uniting the Arabian Peninsula under his leadership through wars and alliances. The Islamic state turned out to be a formula for success: the Islamic conquests that followed brought Persia, the Levant, Egypt, and North Africa under control in barely 30 years. That was an amazing advance. Large areas were lost to the Eastern Roman Empire and the initially Christian population in these areas largely converted to Islam.
Muhammad hadn’t given his succession much care. After his death, things went reasonably well with the first three successors (although two of the three were killed), but then things escalated. Different dynasties contested succession to each other. Initially, the rival dynasties could reasonably argue why they were the logical successor, but gradually even the greatest upstarts claimed the leadership of the caliphate. To date, many a Muslim head of state quietly believes that he himself is the head of the entire Islamic world; the others are actually usurpers, or governors at best. The feelings are of course mutual. It is one of the many reasons why a new pan-Arab caliphate is still a long way off.
Under the dynasty of the Umayyads, the empire expanded even further. At its peak in the 8th century, it included Arabia, Syria, Persia, present-day Pakistan, Egypt, North Africa and the Iberian Peninsula. Under the leadership of Abd al-Rahman, the Umayyads even managed to penetrate deep into France. Eventually, in 732, they were stopped between Poitiers and Tours. The expansion stagnated due to internal problems: the Berbers in Morocco revolted. The Umayyads were forced to withdraw from France to the rear of the Pyrenees. Large parts of the Iberian Peninsula, especially Andalusia, would remain under Islamic rule until 1492.
The Crusades
In the 11th century, the European feudal system was in decline. The Carolingian dynasty was over. In France, the Capetians were in power. In Germany, the Conradines and the Ottonians fought each other. Kings and emperors no longer had a grip on the lower nobility, who were at each other’s throats. Christian knights attacked each other, and the farmers and the church suffered. It could no longer go on like this, thought Pope Urbanus II, and he convened a council in Clermont-Ferrand. Can't you do something useful, he asked the knights. Free the Holy Land from the disbelieving Mussulmen, and you will be in heaven, he promised. Legend has it that the knights roared in unison that it was God's will, they sewed red crosses on their tunics and took their horses from the stable.
There was a mosaic of interests under Urbanus' call. It took a common enemy to keep the knights from bothering each other. And pilgrims complained that they were no longer welcome in Jerusalem. But geopolitics also played a major role. The pope wanted to position himself as the ultimate boss of the Christian world. The battle against the Umayyads in Iberia was well under way, and the invasions of the Vikings and the Asian steppe peoples had become bearable. The loss of the Byzantine army to the Seljuk Turks at the Battle of Manzikert in 1071 prompted the first pleas for aid and troops from the west. The Byzantine emperor had asked the pope for help in reclaiming territory from the Turks. Urbanus saw an opportunity to bind the Eastern Roman Empire to his spiritual authority as well.
Long story short: the first crusade ended in 1099 in a great success. Jerusalem fell, and the knights took control of a vast territory in the Levant. But the success did not last long. Rivalries between the knights and strategic blunders meant that the hold on the Levant was fragile. In 1187, the sultan of Egypt Salah ad-Din recaptured Jerusalem. Renewed attempts to take the holy city failed, and the Crusaders were pushed back to marginal positions.
The Ottoman Empire
A second wave of Islamic expansion came under the Ottomans. After the Mongol devastations of the 13th century, the Arab Empire would not recover, but the Ottoman dynasty soon united the rival jihad-beyliks of the Turks and virtually took over all of the former Caliphate (except Persia, which would become the great Shia rival).
In the 14th century, the Ottomans overran the Byzantine Empire, and Constantinople was finally taken in 1453; it became the capital of the empire. Under Sultan Murat II, the Balkans came under the control of the Ottoman Empire in the years 1430-1448, which it would remain for nearly five centuries. In the 16th century, the Levant also came under control. For centuries, the Ottomans would rule the entire Arab world.
In the 16th century, the growth of the Ottomans seemed unstoppable. In 1529, they stood before the gates of Vienna. Europe was in a state of shock. The relationship with the Turks, and the threat of Islamisation of Europe, occupied everyone's mind. At the same time, the Reformation had begun. The Church of Rome was thus under attack from two sides. Not only did the Reformation force people to reflect on religious coercion and religious toleration, but Turkey's approach to religious diversity also gave food for thought.
As Muslims, the Ottoman sultans claimed only secular power; Muhammad's successors, the khalifas, nominally remained the spiritual and even worldly leaders, but in practice, the sultans called the shots.
For the administration of such a vast empire, the Ottomans had learned a lot from the Roman Empire and their Byzantine successors. It had the structure of a pyramid, with the sultan at its head. Governors had a considerable degree of autonomy, and in the Balkans there was even a degree of self-government for the various ethnicities. Especially if the local population had a clear preference for another god, just as they did under the Romans. Conversion to Islam was encouraged, but generally not enforced.
In the Ottoman Empire, the rot started at the head. There were several candidates from the royal family for succession to the sultans, who first had to gain experience as governor. Whoever did that successfully, qualified. From the 16th century onwards, that system began to deteriorate: it led to violent palace intrigues and fratricides. Corruption paralysed the system, and the royal family became less and less interested in governing the realm, and more in intrigue and physical pleasures. In the middle of the 19th century, large-scale reforms and modernisation, the Tanzimat, were undertaken, but it was already too late: the crumbling of the empire was unstoppable. In World War I, the remnants of the Ottoman Empire collapsed ingloriously.
The Islamic Perspective
Two monotheistic religions came into conflict with each other. Both had a mission: the entire world had to be subjected to their authority. Preferably converted, but on a voluntary basis. Both held a broad interpretation of voluntary conversion. Military expansion was the primal means of spreading their faith for both. A military clash was inevitable.
To understand the Islamic perspective, we need to consider some essential elements of Islam:
The Qur'an originated in the context of the struggle of the Prophet Muhammad in the 7th century CE to bring under his authority two Arab cities: Mecca and Medina.
As a prophet, Muhammad was in direct contact with his god, Allah, but as a chief, he was also a military and worldly leader. This also applied to his successors, the khalifas: although they were not prophets; they were spiritual and worldly leaders. Separation of church and state therefore took on a different interpretation in Islam than in Christianity.
The Qur'an contains a number of clauses on religious expansion and relations with unbelievers that are contradictory, or open to interpretation. But as the word of Allah, only a literal, docile interpretation of the texts is the permissible one in Islam.
The key concept about the expansion of Islam is the word jihad, effort. Jihad is a collective duty of all Muslims, but the scope of that duty is open for discussion. Whether peacefully or combatively, the ultimate goal is clear: the entire world must eventually become devout and professed Muslims.
The Islamic expansion obviously had military and economic motives, but certainly also religious ones. Unlike the Christian expansion, which systematically led to the Christianisation of the conquered barbarian lands, the conversion to Islam of the conquered peoples was not the primary goal. Although it was of course encouraged and there were financial and social benefits associated with it.
Conversion was therefore not a requirement, but submission to the authority of Islam certainly was. The rulers were convinced that imposing Sharia law on the conquered peoples would benefit everyone. The khalifas considered themselves leaders of jihad, which at that time mainly meant: bringing under Islamic rule (dar al-Islam, the house of Islam) the dar al-harb (the house of war, a term for the rule of the disbelievers). Theologically, there is no such thing as peace as long as the whole world is not brought under the rule of Islamic law. Until then, peace is nothing more than a temporary truce.
A just war
To understand the Christian mediaeval attitude towards Islam, we must set aside our image of the Christian continent of Europe for a moment. Large parts of Europe were still far from Christianised. Until the 15th century, hardly anyone had a picture of the Christian continent of Europe in mind; the borders of the Roman Empire were still in everybody’s mind, with the Rhine and the Danube as its northern border. On the other side, in the wasteland, lived primitive savages. The Levant, Asia Minor and North Africa belonged to us! And then suddenly a violent, exotic movement rose from a barren corner of the empire, that Arabian sandbox, and took half of our Christian territory from us! Moreover, knowledge of Islam was virtually nil. Muslims were seen as idolatrous pagans who worshipped Mahomet, the epitome of evil. They had attacked us, seized our territory, so it was war, a fight against evil, until their demise.
The 10th century was a violent century in Europe. Also the 9th, by the way, and the 8th. In fact, the violence had not stopped since the fall of Rome. Knights, vassals in the feudal system, fought each other for a few acres of extra territory. Normans terrorised Europe with their raids. Hungarian tribes wreaked havoc in Central Europe. The Byzantines and the Bulgarians were at each other’s throats in the Balkans. In Iberia, the reconquista was in full swing. Even the pope led his troops into battle.
There was a counter-movement, a peace movement. In any case, leave the church properties undisturbed, and unarmed priests, women and peasants, the bishops advocated at the Council of Charroux. In any case, Christians should lay down their arms on holy holidays, was the consensus. Everyone also agreed that Christians should not fight each other. Only wars with ecclesiastical approval (against the enemies: pagans and muslims) were allowed. In practice, it benefited the pope's power: only he decided who could go to war, and against whom.
But how was the pope to determine that? In the 11th century, theologians rediscovered the just war theory formulated by Augustinus in his magnum opus, De civitate Dei.
Augustinus, of course, could not ignore Jesus and Paulos. Although Jesus mainly preached peace, the existence of a state with its troops was not in question for anyone. State violence and war in the service of God was legitimate.
After all, they are God's servants, and it is their duty to help you. If you do something wrong, you ought to be afraid, because these rulers have the right to punish you. They are God's servants who punish criminals to show how angry God is.
— Paulos of Tarsos, Letter to the Romans 13:4
And while violence by individuals was not propagated, Augustinus believed that Christian states need not hold back. They were allowed to use force to keep the peace and fight crime.
They who have waged war in obedience to the divine command, or in conformity with His laws, have represented in their persons the public justice or the wisdom of government, and in this capacity have put to death wicked men; such persons have by no means violated the commandment, "Thou shalt not kill."(...) But, say they, the wise man will wage just wars. As if he would not all the rather lament the necessity of just wars, if he remembers that he is a man; for if they were not just he would not wage them, and would therefore be delivered from all wars. For it is the wrongdoing of the opposing party which compels the wise man to wage just wars
— Augustinus Hipponensis, De civitate Dei (413-426), Book I, chapter 21; Book XIX, chapter 7
It still sounded rather theoretical, and it expresses the anguish that seems typical for Augustinus. Tomasso d'Aquino was more practical; in 1265 he further elaborated the conditions under which a just war (bellum justum) could be waged:
Legitimate authority. A just war must be declared by an authority representing the common good, ultimately aiming at peace under God.
Righteous purpose. War must have a good and just aim. It does not include self-interest, power, or wealth; retaliation or reconquest is.
Right intention. Achieving peace must be central, even at the height of armed struggle.
Conquests of pagan territories were routinely justified as self-defence. But the aggression could not start from the Christian world: it could only be in response to a pagan provocation or invasion. In that case a papal bull was available, in which the war was agreed upon.
Crusades were also considered bellum justum. Crusades usually started with a summons by the pope; thus the legitimate authority was obtained. The goal was righteous: the reconquest of Jerusalem. That was the city of Jesus after all, there could be no misunderstanding about that. It did not occur to Tomasso that plenty of other people had also put soul and bliss in that city. One is right, so the other must be wrong, that was typical mediaeval reasoning. And the fighters' intention was right, because it was religiously motivated. All clear.
Canon law, especially the Decretum Gratiani and the Decretales of Pope Gregorius IX, both from c. 1140, prescribed religious toleration. No forced conversion, no killing, and the religion of others had to remain undisturbed. This was true for Jews, but also for Muslims. However, a special situation applied to the Muslims, because the Christian states considered themselves at war with the Islamic states. Then, violence was justified. But Muslims under the rule of a Christian state should be left alone if they behaved peacefully.
However, this view was not put into practice after the reconquest of Spain from the Moors in the late 15th century. With the help of the Inquisition, the local population, usually Muslim for centuries, was forced en masse to convert to Christianity. Jews and inveterate Muslims could pack their bags. You see: no forced conversion. They just had to scram, that's all.
The war against the Turks also became a hot topic for the intelligentsia of the time. Martin Luther gradually became more interested in the subject and began to study Islam, eventually leading to a Latin translation of the Qur'an in 1543. He wrote seven works on the Turkish question, including Vom Kriege wider die Türken (1529). The Turks came to conquer what did not belong to them, and the god of the Turks was the devil. He considered a war against the Turks justified, even necessary. He even saw parallels with the apocalyptic vision in the Bible book of Daniel; the incursions of the Turks were therefore part of God's plan. But the war had to be accompanied by prayer and penance. After all, the Christians had themselves to blame for the Turkish invasions because of their sinfulness. Luther wanted to warn Christians against the dangers of Islam. He knew that many Christians in the Ottoman Empire eventually became Muslims, and he wanted to arm the Christians against this pernicious influence.
Erasmus also thought the war against the Turks was justified. In his publication Considerations on starting a war against the Turks (1530) he passingly added two more demands to Tomasso’s conditions for a bellum justum:
War should also be the last resort; all other options should be tried first.
And a war is only justified in self-defence.
Well, those Turks, those were the aggressors, that should be clear. Although Turks were barbaric outlaws, he made their faith an example to the disinterested and divided Christians:
Those we call Turks are largely semi-Christians and probably closer to true Christianity than most of us.
— Desiderius Erasmus, Utilissima consultatio de bello Turcis inferendo (1530)
Erasmus, nuanced as always, gave a reservation. If a Christian thought that he was free to butcher a Turk like a mad dog for nothing but that he was a Turk, he was wrong. He would not escape his just punishment. Turks could only be lawfully convicted by the Christian authorities if they violated the law to which they too were subject. So not because of their religion or simply for being Turkish.
Colliding worlds
To summarise: Islam and Christianity were both expansive, but had different goals, and different justifications.
Islamic rulers didn’t need justification. The goal was the establishment of the laws of Islam in the conquered territories. That sufficed as justification. Forced conversion, forbidden in Islamic law, was generally not prevalent. Systematic favours for Muslims in the conquered territories nevertheless ensured that many Christians ultimately made the best of a bad bargain.
Christian rulers had to deal with a theological doctrine of just war: wars could only be engaged in defence. Even Carolus Magnus, a ruthless conqueror, bent over backwards to justify his attacks on pagan peoples. Trickery, distortion of the truth, provocations and false flag operations were part of the arsenal to justify wars of conquest as self-defence or provoked attacks. Also for the conversion of pagans, Christian kings applied methods that they could sell as urge, not coercion. Those were obstacles to reconcile Christian aggression with Jesus’ peaceful instructions. Christian toleration taught Europe its duplicity.
For further reading
Augustinus Hipponensis, De civitate dei (426), also in English
Tomasso d’Aquino, Summa theologiae (1265)
Martin Luther, Vom Kriege wider die Türken (1529), also in English
Desiderius Erasmus, Utilissima consultatio de bello Turcis inferendo (1530)
Denys Hay, Europe: the emergence of an idea (1957/1968)
Thomas Bokenkotter, A concise history of the catholic church (1978/2005)
Bernard Lewis, Politics and war, in: Joseph Schacht, Clifford Edmund Bosworth (ed.), The legacy of islam (1974)
Pierre Riché, Les Carolingiens: une famille qui fit l’Europe (1983)
Bassam Tibi, War and peace in Islam, in: Sohail Hashmi (ed.), Islamic political ethics: civil society, pluralism, and conflict (2002)
Mark Cartwright, Crusades, World History Encyclopedia (2018)
Syed Muhammad Khan, Umayyad dynasty, World History Encyclopedia (2020)
Syed Muhammad Khan, Ottoman empire, World History Encyclopedia (2020)
This was the eighth newsletter in the series on Toleration and Christianity. The episodes so far are:
Before Christ
Jesus of Nazareth had some exceptionally tolerant ideas. In order to understand them, we need to know more about Jesus's Jewish background: the history of the Jewish people, their god and their law.Where Jesus' tolerant ideas came from
In some ways, Jesus was a tolerant thinker. But he didn't have all his views of his own. About Jesus' simple origins, the halakhic tradition and Hellenic influences.How this contrarian apostle accidentally founded a world religion
About the tragic life and the miraculous survival of Paulos of Tarsos, the orphaned Jesus community in Jerusalem, the mission in the pagan West and the irrelevance of the Jewish Law.No Jewish law for Christians, but what then?
Why Christian law is not in the Bible. About Paulos's selective application of Jesus' instructions, and his remarkable views on sex, women, and men with long hair.With blood on their hands and tears in their eyes
In the 4th century, the Church of Rome gained power and lost its innocence. The unity of the church became the main thing, and heresy a sin. After Augustinus’ struggle, the church got a killer instinct.Christianity, slavery and the conversion of pagans
On conversion of pagans without compulsion. And Christian approval of slavery. About sex slaves, the conversion of a tourist paradise, and exploitation by the village priest.The clean hands of the Church, the dirty hands of the State
How the popes let the Christian monarchs do the dirty work. But separation of church and state later came to mean something else: a secular government.The just war against Islam
A clash between Christianity and Islam was inevitable. Not only because they got into each other's way, but also because they used different justifications for warfare.