Throughout history, Christianity has been invoked to justify numerous wars, crusades, and violent campaigns—often in stark contradiction to the faith’s central teachings of peace, love, and “turning the other cheek.” From the early medieval period through the modern era, these conflicts have shaped nations, redrawn borders, and left millions dead in their wake.
The Crusades: Holy Land bloodshed (1095-1291)
When Pope Urban II called for the First Crusade in 1095, he unleashed nearly two centuries of intermittent warfare justified by Christian zeal. Supposedly launched to reclaim Jerusalem and the Holy Land from Muslim control, the Crusades exemplified how religious fervour could be harnessed for political and territorial gain.
The First Crusade succeeded in capturing Jerusalem in 1099, but what followed was a massacre that contradicted Christian principles of mercy and compassion. Crusaders slaughtered Muslims and Jews indiscriminately—men, women, and children—until, according to contemporary accounts, knights rode through blood reaching their horses’ knees.
As the Crusader knight Fulcher of Chartres wrote: “In the Temple of Solomon, the crusaders rode in blood up to their bridles. Indeed, it was a just and splendid judgment of God that this place should be filled with the blood of the unbelievers.”
Later Crusades proved less “successful,” and by 1291, Muslims had recaptured all Crusader territories. The legacy included:
- Deepened religious animosity between Christians and Muslims
- Weakening of the Byzantine Empire
- Expansion of European trade networks
- Emergence of military orders like the Knights Templar
- Increasing papal power and religious intolerance within Europe
The Reconquista: Spain’s religious purge (718-1492)
For nearly 800 years, Christian kingdoms in the Iberian Peninsula waged a series of campaigns against Muslim-controlled territories. The Reconquista culminated in 1492 when Ferdinand and Isabella conquered Granada, the last Muslim stronghold.
Although portrayed as a holy mission to reclaim Christian lands, the Reconquista’s religious justification masked territorial and political ambitions. Its conclusion led to:
- Forced conversions of Muslims and Jews
- The Spanish Inquisition’s persecution of suspected non-Christians
- Expulsion of Jews and Muslims who refused conversion
- Unification of Spain under Catholic monarchs
The aftermath of the Reconquista demonstrates how religious warfare often leads to religious persecution. Despite Jesus’s teachings of tolerance, Spanish Christians created systems to root out and punish “heretics” and those suspected of secretly practising other faiths.
European wars of religion: Christians against Christians (16th-17th centuries)
Following the Protestant Reformation, Europe erupted in a series of devastating conflicts between Catholics and various Protestant denominations. These wars represented perhaps the most striking divergence from Christ’s message of unity among believers.
The Thirty Years’ War (1618-1648)
Beginning as a conflict between Protestant and Catholic states within the Holy Roman Empire, the Thirty Years’ War evolved into Europe’s most destructive religious conflict. The war was triggered by the famous “Defenestration of Prague” in 1618 when Protestant nobles threw Catholic officials out of a window in Prague Castle.
The Habsburg Emperor Ferdinand II played a decisive role in starting the conflict. A fervent Catholic educated by Jesuits, Ferdinand once declared he would “rather rule over a desert than a land of heretics.” As King of Bohemia, he had revoked religious freedoms guaranteed by the Letter of Majesty and closed Protestant churches in Prague, directly provoking the Protestant rebellion.
Throughout the war, Ferdinand’s uncompromising religious policies—including the 1629 Edict of Restitution demanding Protestants return all church properties acquired since 1552—escalated tensions and expanded the conflict. What began as a religious dispute in Bohemia became a devastating continental war. An estimated eight million people died from combat, famine, and disease. In some regions, up to 60% of the population perished.
The Peace of Westphalia ending the war established the principle that rulers could determine their territories’ religion, essentially acknowledging that religious unity in Europe was impossible.
French wars of religion (1562-1598)
For 36 years, France suffered through eight civil wars between Catholics and Protestant Huguenots. The conflict was catalysed by the growth of Calvinism in France during the 1550s, which alarmed the Catholic establishment. The spark that ignited open warfare came in March 1562, when the Duke of Guise and his armed retinue massacred a congregation of Huguenots worshipping in a barn at Wassy (Vassy). This act of violence transformed simmering tensions into armed conflict.
The wars were marked by shifting alliances among powerful noble families—particularly the Catholic Guise family and the Protestant Bourbons—who used religious division to advance their political ambitions. The conflict reached its nadir with the St. Bartholomew’s Day Massacre, which began in Paris on 24 August 1572. Following the wedding of the Protestant Henry of Navarre (future King Henry IV) to Margaret of Valois, Catholic mobs began systematically murdering Protestants throughout the city.
The violence was instigated by Catherine de’ Medici, the queen mother, with the approval of her son King Charles IX. Catherine had grown alarmed at the influence of Protestant leader Admiral Gaspard de Coligny over the young king. What began as a targeted assassination of Huguenot leaders spiralled into mass violence that spread from Paris to other French cities. Estimates of the death toll range from 5,000 to 30,000 Protestants killed over several weeks.
King Henry IV, himself a Protestant who converted to Catholicism to secure the throne, finally ended the conflicts by issuing the Edict of Nantes in 1598, granting Protestants limited religious freedoms—though these would later be revoked by Louis XIV in 1685.
English Civil War (1642-1651)
While often portrayed primarily as a constitutional struggle between Parliament and the Crown, the English Civil War was deeply influenced by religious tensions. King Charles I’s perceived Catholic sympathies—including his marriage to Catholic Henrietta Maria of France and attempts to impose high-church Anglican practices—alarmed the more Puritan-leaning Parliament and common people. Many Puritans viewed the elaborate rituals promoted by Archbishop William Laud as dangerously close to Catholicism, which they considered idolatrous.
The conflict pitted Parliamentarians (or “Roundheads”), who were predominantly Puritan in religious outlook, against Royalists (or “Cavaliers”), who supported the king and the Anglican church hierarchy. Oliver Cromwell emerged as the Parliament’s most effective military leader, forming his “New Model Army” that was infused with Puritan zeal. Cromwell and many of his soldiers viewed themselves as God’s instruments, fighting against ungodly forces—a belief that strengthened their resolve in battle.
Following Parliament’s victory and Charles I’s execution in 1649, Cromwell’s subsequent rule as Lord Protector saw religious reforms in England but brutal religious persecution elsewhere. His campaign in Ireland (1649-1650) was particularly savage, justified by both political rebellion and religious differences. The massacres at Drogheda and Wexford, where Catholic civilians and priests were slaughtered alongside combatants, were defended by Cromwell as “a righteous judgment of God upon these barbarous wretches.” These atrocities cemented centuries of religious-tinged animosity between Ireland and England.
The Restoration of the monarchy in 1660 did not end England’s religious tensions. The Test Acts and various religious settlement laws continued to discriminate against both Catholics and Protestant dissenters until the 19th century. The religious dimensions of the English Civil War had lasting consequences for British politics, constitutional development, and imperial policies.
The Northern Crusades: Forced conversion (12th-13th centuries)
While the better-known Crusades targeted the Holy Land, the Northern Crusades focused on forcibly converting pagan peoples around the Baltic Sea. These campaigns were launched in 1147 when Pope Eugene III extended the crusading concept to the northern frontier of Christendom, authorising campaigns against the pagan Wends (Slavic peoples living east of the Elbe River).
The catalyst for this expansion of crusading was the failure of the Second Crusade in the Holy Land, which prompted European leaders to seek more achievable victories against pagans closer to home. Bernard of Clairvaux, the influential Cistercian abbot who had preached the Second Crusade, declared: “We utterly forbid that for any reason whatsoever a truce should be made with these peoples, either for the sake of money or for the sake of tribute, until such a time as, by God’s help, they shall be either converted or wiped out.”
Multiple groups participated in these northern holy wars:
- Danish and Swedish kings launched campaigns against Finns, Estonians, and other Baltic peoples
- German princes from Saxony and Holstein attacked the Wends and other Slavic peoples
- The Livonian Brothers of the Sword, a military order founded in 1202, conquered parts of modern Latvia and Estonia
- The Teutonic Knights, originally formed during the Crusades to the Holy Land, became the dominant force in the region after 1226 when they began conquering Prussia
- Polish dukes collaborated with the Teutonic Knights against the pagan Prussians before later coming into conflict with the Knights themselves
The methods employed were brutally effective. The Teutonic Knights systematically conquered territory, built castles, brought in German settlers, and forced conversion of local populations. Those who resisted were often killed or enslaved. The Chronicle of Henry of Livonia describes campaigns where villages were burned, men killed, and women and children taken captive, all in the name of spreading Christianity.
These campaigns directly contradicted Christ’s approach to spreading his message through peaceful persuasion. The Northern Crusades resulted in:
- Mass killings and forced baptisms
- Destruction of indigenous cultural and religious traditions
- German colonisation of Baltic territories
- Establishment of new Christian states in northeastern Europe
- Creation of a frontier society dominated by military orders and colonial settlers
By the end of the 13th century, paganism had been largely eliminated from the Baltic region through these violent campaigns, completing the Christianisation of Europe through means starkly at odds with the peaceful message of the Gospel.
The Albigensian Crusade: Christians killing Christians (1209-1229)
Colonial Conquests: The Cross and the Sword
European colonisation often intertwined Christianity with imperial conquest. Spanish conquistadors in the Americas, Portuguese explorers in Africa and Asia, and later colonial powers frequently justified their conquests as spreading Christianity.
In the Americas, Indigenous populations were decimated by disease, warfare, and forced labour, all while colonisers claimed to be saving souls. Bartolomé de las Casas, a Dominican friar who witnessed these atrocities, wrote: “What we committed in the Indies stands out among the most unpardonable offences ever committed against God and mankind.”
Modern Religious Conflicts
Even in recent times, Christianity has been invoked to justify violence:
- In Northern Ireland, the Troubles (1968-1998) pitted Protestants against Catholics in a conflict that claimed over 3,500 lives
- In Bosnia, some Christian Serbs committed atrocities against Bosnian Muslims in the 1990s, justifying ethnic cleansing with religious rhetoric
- In Central Africa, the Lord’s Resistance Army claimed Christian inspiration while committing horrific human rights abuses
The contradiction of Holy War
Perhaps the most profound aspect of wars fought in Christianity’s name is their fundamental contradiction with Jesus’s core teachings:
- “Love your enemies, do good to those who hate you” (Luke 6:27)
- “Blessed are the peacemakers, for they will be called children of God” (Matthew 5:9)
- “Put your sword back in its place, for all who draw the sword will die by the sword” (Matthew 26:52)
The early Christian church was largely pacifist for its first three centuries. Only after Christianity became Rome’s state religion did theologians like Augustine develop “just war” theories that allowed Christians to fight under certain circumstances.
Lessons from blood-stained history
The history of wars fought in Christianity’s name serves as a sobering reminder of religion’s potential for both inspiration and corruption. These conflicts demonstrate how readily foundational teachings of peace can be set aside when political power, territorial ambition, and human fear of difference come into play.
This historical accounting is not meant to single out Christianity—virtually all major religions have been used to justify violence at various points. Rather, it highlights the universal human tendency to corrupt spiritual teachings for worldly purposes.
The legacy of these wars continues to influence global politics, interfaith relations, and cultural identities today. By acknowledging this complex and often troubling history, Christians and non-Christians alike can work toward ensuring that religion serves as a force for peace rather than a justification for violence.
