Judaism and Christianity share a virtue easy to overlook, because it shows up as an absence rather than a doctrine. Neither tradition's founding texts authorize a standing program of holy war for the sake of expanding the faith itself. Deuteronomy commands a war of conquest, but one bound to seven named nations and a single generation, closed by the very tradition that received it once those nations could no longer be identified. Christianity's first three and a half centuries produced no theology of conquest at all, and the just war framework it eventually built from Roman inheritance was a doctrine of restraint, not expansion.
A shared restraint like this is easiest to see against a genuine alternative. Islam's classical jurisprudence built something neither Judaism nor Christianity had produced on its own, a standing legal category obligating the faithful to expand the territory of the faith, carrying no closing clause. Held up against that contrast, what Judaism and Christianity share stops looking like an accident of history and starts looking like a shared inheritance worth naming.
A War With a Closing Date
Deuteronomy's language is severe by design. The text commands the destruction of seven named nations occupying the land promised to Abraham's descendants, listing them without ambiguity: "the Hittites, and the Girgashites, and the Amorites, and the Canaanites, and the Perizzites, and the Hivites, and the Jebusites" (Deuteronomy 7:1). This is ḥerem, devotion to destruction, a ritual-legal category rather than a general theology of holy war. Its boundaries sit inside the text itself. Deuteronomy 20 draws the line explicitly. A city outside the promised land receives an offer of peace before any siege begins, and only the seven named nations within the land fall under the total ban. Scholars have long used the term "holy war" for these chapters, following Gerhard von Rad's classic study of the category, but the label describes a bounded military institution tied to a single generation's entry into a specific territory, not an open program for the religion's expansion.
Rabbinic tradition treated that boundary as load-bearing rather than decorative. Maimonides rules in the Mishneh Torah that the commandment to destroy the seven nations no longer applies, because their identity was lost when the Assyrian king Sennacherib scattered and intermingled the ancient peoples of the region, leaving no way to determine who they were. A commandment that cannot identify its object cannot be fulfilled, and the tradition drew the obvious conclusion. Moshe Weinfeld and Michael Walzer, working from different angles, both read Deuteronomy's conquest as a closed historical episode tied to Israel's specific entry into a specific land. The boundary held; no later generation treated it as license for war against other peoples, in other lands, for other reasons.
One episode complicates any claim that Jewish history stayed entirely clear of conquest for the sake of conversion, and it deserves a direct answer rather than a quiet omission. Around 125 BCE the Hasmonean ruler John Hyrcanus conquered Idumea and imposed circumcision and Jewish law on its population as a condition of remaining on their land, a policy his successor Aristobulus I extended to Galilee. Josephus records the episode as compulsion. It sits outside anything Deuteronomy commands, outside anything the rabbis who followed treated as a model, and it produced no doctrine, no legal category, and no second instance. What it produced instead was discomfort, most visibly in the lasting suspicion directed at Herod for his Idumean ancestry generations later. A single contested episode carried out by a Hellenizing dynasty and repudiated in memory is a different creature from a standing legal category commanding open-ended expansion.
Four Centuries Without a Sword
Whatever Christianity became, its earliest centuries record a faith spread by persuasion rather than conquest. Its central figure told a follower reaching for a weapon in his defense that "all they that take the sword shall perish with the sword" (Matthew 26:52), and told his own followers, "Love your enemies, bless them that curse you" (Matthew 5:44), a command aimed at persuasion rather than subjugation. Paul described the church's methods to the Corinthians in terms that rule out physical force altogether: "the weapons of our warfare are not carnal, but mighty through God" (2 Corinthians 10:4). For roughly three centuries, the movement that carried this teaching spread through preaching, through the ordinary movement of merchants and travelers across the Roman world, and through a willingness to die under persecution that Roman writers themselves found remarkable. Nothing in the record from this period describes an army raised to convert a people, a doctrine authorizing one, or a theologian arguing that one should exist.
Constantine's conversion in the early fourth century changed the church's relationship to power without immediately producing a theology of conquest. What followed was legal coercion within an empire the church now shared, the closing of pagan temples and the Theodosian decrees against sacrifice late in that same century, coercion aimed inward at populations already inside Roman borders rather than campaigns of conquest aimed outward to expand the faith's reach. The distinction matters because it shows how gradually and how late the fusion of Christianity with organized warfare occurred, a full three and a half centuries after the crucifixion, and how narrow its first form was when it finally arrived.
Rome Supplies What the Gospels Left Unaddressed
Augustine gave Christianity its first serious theology of war in the early fifth century, in City of God and in his polemic against the Manichaean Faustus, and what he built was corrective rather than expansionary. War, for Augustine, required legitimate authority, a just cause, and a right intention aimed at restoring peace, criteria that restrain the use of force and address a narrower question, how a church now entangled with a Christian empire should think about the violence that empire regularly practiced. Augustine's framework authorizes no war for the purpose of spreading the faith to unconquered peoples, and it promises the fighter no spiritual reward for killing in God's name. It is a theory of restraint, borrowed from Roman legal and philosophical categories and grafted onto Christian ethics, aimed at limiting wars already underway rather than authorizing new ones for the faith's expansion.
Augustine's just war survives largely intact as a restraining doctrine for six more centuries, an inheritance from Rome's statecraft rather than from Christianity's own founding texts, recognizable as an import precisely because nothing native to the Gospels or the Epistles had called for it in the first place. That transformation required a different kind of pressure, one that arrived from outside Christendom rather than from within its own texts.
The Contrast That Makes the Restraint Visible
Islam's early conquests, beginning in the 630s, reached within a single century from the Hijaz through Persia, the Levant, North Africa, and into Iberia. Byzantium and Persia posed no existential threat to the Hijaz at the time, and the historiography, Fred Donner's standard treatment included, explains the conquests through religious conviction and opportunity rather than danger to Arabia itself. What the conquests produced, beyond territory, was a legal category. Majid Khadduri's standard treatment of the doctrine describes a framework dividing the world into the abode of Islam and the abode of war, treating the expansion of the first at the expense of the second as a standing religious obligation rather than a single bounded campaign against named peoples in a named land. Classical jurists disagreed among themselves about how unconditioned that obligation truly was, a genuine debate John Kelsay has documented, but the dominant historical practice across the early centuries applied the unconditioned reading against Zoroastrian Persia, Christian Byzantium, and every other neighbor within reach.
Surah 9, commonly called the Sword Verse at its fifth verse, instructs believers to "kill the polytheists wherever you find them" once a truce period has expired, with an exception written into the same verse for those who repent, pray, and give alms (Quran 9:5). Classical exegetes nonetheless read the verse in maximal terms. Ad-Dahhak ibn Muzahim, preserved in Ibn Kathir's tafsir on the verse, held that it abrogated every treaty of peace between Muhammad and any idolater, and Ibn 'Abbas is recorded holding that no idolater retained any covenant of safety once the verse was revealed. Twenty-four verses later, the same surah turns from the polytheists of Arabia to the People of the Book directly, commanding believers to fight Jews and Christians who reject Islam's terms "until they give the jizyah willingly while they are humbled" (Quran 9:29). A hadith graded authentic and preserved in both Sahih al-Bukhari and Sahih Muslim states the underlying logic plainly. On the authority of Ibn 'Umar, Muhammad is reported to have said he had been commanded to fight the people until they testified there was no god but Allah, established prayer, and paid the required alms, at which point their blood and property became protected (Sahih al-Bukhari 25). Muslim scholars across the centuries have debated how far this logic extends and under what conditions, the same internal debate Kelsay documents. What sits outside serious dispute is that the mainstream classical tradition, not a reading invented by outside critics, built a standing legal category directly out of these texts.
Conquest itself was nothing new in the seventh century. What was new, and what neither Deuteronomy's closed campaign nor the Gospels' silence had anticipated, was a codified doctrine with no expiration built into its own architecture. That is the alternative Judaism and Christianity's shared restraint has to be measured against to be seen clearly at all.
A Model Too Distant to Rival
René Girard's account of mimetic desire supplies the precise mechanism for what happened next, and the mechanism matters because it explains why Christendom absorbed this particular pattern rather than some other one. Girard distinguished two ways a model shapes what an imitator wants. In external mediation, the model sits outside the imitator's reach, distant in geography or standing, admired and copied without becoming a rival, because the two desire different things entirely. In internal mediation, the model enters the imitator's own field of action, comes to be desired for the same object the imitator wants, and the relationship curdles into rivalry, each side coming to resemble the other more than either would admit.
For roughly a century after Islam's emergence, Christendom's relationship to it was external mediation in its purest form, and the imbalance behind that relationship is worth stating plainly. The Abbasid Caliphate by the eighth century was the preeminent power of the age, its capital at Baghdad wealthier, larger, and more scientifically and administratively sophisticated than anything Western Christendom could produce. Charlemagne fought Muslim forces in Spain in 778, and by the 790s his court was in active diplomatic exchange with Harun al-Rashid's Baghdad, an exchange that culminated in 802 with the arrival of the elephant Abul-Abbas after a journey of years through Egypt and North Africa. Frankish chroniclers treated the Caliphate as a power worth courting rather than a rival to be matched. That relationship carried no theological contagion, because Charlemagne's Francia and Harun al-Rashid's Baghdad wanted different things entirely. Francia had nothing Baghdad wanted, and admiration of Baghdad's power produced diplomacy, not doctrine.
The Model Becomes a Rival
Iberia changed the equation entirely. The Umayyad conquest of 711 placed a Christian population under direct Muslim rule for what would become nearly eight centuries, and for the first time Christendom and the Islamic world wanted the same specific object, the same land, the same cities, the same sacred ground. That is exactly the condition internal mediation requires, a model now close enough, and now competing for the same territory, to become a rival rather than a spectacle. The long counter-effort to reverse Muslim rule in Iberia, well ahead of anything the Holy Land would later produce, is where Christian holy war first acquired its institutional shape. Pope Alexander II granted a collective indulgence to participants in an expedition against the Muslim-held city of Barbastro in 1064, three decades before Urban II's sermon at Clermont, and the Cluniac reform movement actively encouraged Christian knights to direct their violence against Muslim Iberia rather than against each other. The Reconquista fused pilgrimage, penance, and armed conflict into a single religiously rewarded enterprise, structurally identical to what Islamic doctrine had already institutionalized, standing warfare waged in God's name with spiritual reward promised to the fighter. Christendom had no native category for that fusion and built one only after centuries in direct contact with the doctrine that did.
The Crusades exported that fusion east under genuine provocation. The Fatimid destruction of the Holy Sepulchre in 1009, the Seljuk victory at Manzikert in 1071 that closed pilgrimage routes, and Byzantine appeals for help against an advance that now threatened Constantinople itself all supplied the occasion for Urban II's call in 1095. Historians rightly note that internal European developments, Carl Erdmann's classic study among them, did real work building the theological machinery the Crusades would use. That internal account leaves a real question standing, why Christendom needed that machinery in the first place, and why it reached for conquest narratives like Joshua that its own tradition had already closed centuries earlier rather than leaving them closed. Girard's theory answers both. Once the model became a rival, Christendom had no need to borrow Islamic texts in order to borrow Islam's pattern. It reached backward into its own scriptural inheritance to authorize a practice it had not originated, which is precisely what internal mediation produces, an imitator convinced that a borrowed desire is an autonomous one.
The doubling this produced ran in both directions, and the clearest evidence for it comes from Islam's own history rather than from Christendom's. Carole Hillenbrand's history of the Crusades from Islamic sources argues that offensive jihad as an actively mobilizing doctrine had grown comparatively dormant across much of the Muslim world by the time the Crusades began, and that it was deliberately revived as a unifying instrument of propaganda under Nur al-Din and then Saladin, specifically in response to the Crusader presence in the Levant. A doctrine Christendom had absorbed from Islam was, within a century, reactivated by Islam in direct response to Christendom's absorption of it. That loop, model to imitator to rival to remodeled model, is the mimetic crisis Girard describes, two systems in sustained contact converging on the same practice, each certain its own escalation grew from its own tradition alone, each becoming what Girard would call a double of the other, structurally identical in function while insisting on total difference in origin.
The Same Pattern Crosses the Ocean
The theology that reached the Americas in the sixteenth century was Iberian before it was universal, shaped by eight centuries of contact with Islamic rule before it crossed an ocean at all. The Requerimiento, the declaration Spanish conquistadors were required to read to indigenous populations in 1513 before waging war against them, offered submission to the Christian faith and the Spanish crown as an alternative to conquest, and treated refusal as grounds for legitimate war, a structure historian Patricia Seed traces directly to the legal and theological habits Spain had developed across the Reconquista. The encomienda system that followed, extracting tribute and labor from conquered populations in exchange for nominal religious instruction, mirrors the administrative logic Christian Iberia had already practiced on Muslim and Jewish populations at home. What crossed the Atlantic was a theology already several centuries removed from anything Jesus, Paul, or the church's first martyrs had taught, an import wearing a cross rather than a native growth of the tradition that carried it.
An Inheritance Worth Naming
None of this touches the substance of the theological disagreement between Judaism, Christianity, and Islam over prophecy, covenant, and the identity of the messiah. Those disagreements are old, serious, and worth pursuing on their own terms. What the history of conquest theology settles is narrower, and for that reason more useful as a shared claim rather than a competitive one. Deuteronomy's conquest was bounded by design and closed by the very tradition that received it. Christianity's first three and a half centuries produced no comparable doctrine at all, and the just war theory it eventually built was a theology of restraint borrowed from Rome, not a native development of its own texts.
Held up against Islam's genuine invention, a standing legal category with no closing clause, that shared restraint stops looking incidental. It looks like an inheritance Judaism and Christianity share in fact, obscured for centuries by the fact that Christendom spent several of those centuries absorbing a foreign pattern before recognizing it as foreign. Naming the contrast plainly serves every tradition it touches, including the one that supplied the pattern being named. It is simply what makes the shared inheritance visible in the first place.
Primary Texts
- Augustine. City of God and Contra Faustum. Translated by Marcus Dods. In Nicene and Post-Nicene Fathers, First Series, Volume 2, edited by Philip Schaff. CCEL.
- Ibn Kathir, Isma'il. Tafsir al-Qur'an al-'Azim, commentary on Surah 9:5. Quran.com.
- Josephus, Flavius. Antiquities of the Jews, Book 13.
- Maimonides. Mishneh Torah, Laws of Kings and Wars 5:4. Sefaria.
- The Quran. Sahih International translation. Quran.com.
- Sahih al-Bukhari and Sahih Muslim. Sunnah.com.
- Scripture citations follow the King James Version via Bible Gateway.
Secondary Literature
- Donner, Fred M. The Early Islamic Conquests. Princeton: Princeton University Press, 1981.
- Erdmann, Carl. The Origin of the Idea of Crusade. Translated by Marshall W. Baldwin and Walter Goffart. Princeton: Princeton University Press, 1977.
- Girard, René. Violence and the Sacred. Translated by Patrick Gregory. Baltimore: Johns Hopkins University Press, 1977.
- Hillenbrand, Carole. The Crusades: Islamic Perspectives. Edinburgh: Edinburgh University Press, 1999.
- Khadduri, Majid. War and Peace in the Law of Islam. Baltimore: Johns Hopkins University Press, 1955.
- Kelsay, John. Arguing the Just War in Islam. Cambridge, MA: Harvard University Press, 2007.
- Seed, Patricia. Ceremonies of Possession in Europe's Conquest of the New World, 1492–1640. Cambridge: Cambridge University Press, 1995.
- von Rad, Gerhard. Holy War in Ancient Israel. Translated by Marva J. Dawn. Grand Rapids: Eerdmans, 1991.
- Walzer, Michael. In God's Shadow: Politics in the Hebrew Bible. New Haven: Yale University Press, 2012.
- Weinfeld, Moshe. Deuteronomy and the Deuteronomic School. Oxford: Clarendon Press, 1972.
