In the blistering heat of 15 July 1099, 10,000 European Crusaders broke through the walls of Jerusalem. Thousands of men, women, and children sought refuge in the al-Aqsa Mosque, one of Islam’s holiest sites – to no avail. The invaders threw some off the high walls to their deaths; the rest they butchered.

When the massacre was over, the self-styled “pilgrims” held a thanksgiving service at the ancient Church of the Holy Sepulchre – traditionally regarded as the site where, a millennium earlier, Jesus of Nazareth had died on a Roman cross, refusing violence and calling his followers to love their enemies.

Raymond of Aguilers, a chronicler of the First Crusade, captured the mood: “men rode in blood up to their knees and bridle reins. Indeed, it was a just and splendid judgment of God … This day, I say, marks the justification of all Christianity.”

Christianity’s violence problem

The history of the West has been mostly Christian. And it’s certainly been violent – Crusades, inquisitions, wars of religion …

So does religion cause war? Would the world be a more peaceful place without it?

“I’m ashamed that the name of Christ has ever been associated with a bomb or an AK47.”

John Lennox, University of Oxford

Love your enemies

Violence is, tragically, a human universal. But what makes atrocities perpetrated by Christians especially shocking is their stark contrast with the teachings and example of the founder of the Christian faith: Jesus.

Jesus preached a radical message of love for enemies. “Do good to those who hate you,” he said. “If someone slaps you on one cheek, turn the other also.”

When he was arrested, he refused to fight back. Even while being nailed to a Roman cross, he prayed that his executioners would be forgiven.

It was a demanding – and, on the face of it, deeply impractical – ethic. But his followers, for the first few centuries after his death, took it seriously.

So what happened?

How did Christians go from being the persecuted to the persecutors? How did they get from “love your enemies” to “holy war”?

It all has to do with the shift that comes about when Christians go from being a persecuted minority to an influential social group – even to wielding state power.

As time went on, Christians had to think through whether it was ever legitimate to wage war, and came up with some grudging concessions that became known as “just war” theory. There were also medieval initiatives like the so-called “Truce of God” and “Peace of God”, which aimed to limit or at least channel the violence of the European warrior class.

These efforts met with some success – but they also had some unexpected consequences.

“In one sense, the reason why Christian history contains so much coercion is simply because it has been so unchristian. There is an irony – to put it very mildly – in following the Prince of Peace, who explicitly abjures violence, violently.”

Nick Spencer, Theos Think Tank

The Crusades are one of the most notorious episodes of Christian history.

These were a series of military expeditions organised by Western European Christians, predominantly to combat Muslim expansion in the East.

The First Crusade kicked off in 1095 when Pope Urban II responded to pleas for help from the Christian emperor of Byzantium (modern-day Istanbul) by issuing a decree: whoever took up the sword to defend their Eastern brethren and retake the Holy Land would receive a pardon for their sins. This was something new and distinctive in warfare … salvation for taking up the sword.

While the First Crusade mostly achieved its goals, capturing Jerusalem in 1099, later efforts ranged from only partially successful to downright disastrous. These “holy wars” were launched intermittently for centuries – and not always against foreign powers. The Albigensian Crusade (1209-1229) was directed against enemies much closer to home. A twenty-year military campaign against a group of perceived heretics in southern France, it was exceptionally brutal, even by the standards of the time.

The Spanish Inquisition lasted for 350 years. It existed to identify “heretics” and enforce religious orthodoxy.

It’s perhaps the most horrific example in history of the church trying to control people and coerce belief.

Inquisitions or heresy trials took place across Europe during the medieval and early modern period, but none was more sustained – or more feared – than the Spanish Inquisition.

Most of the mental images we associate with this history are part of what historians call the “Black Legend” of the Spanish Inquisition – stories of torture and abuses of power that were basically invented by Protestants from the 16th century onwards as anti-Catholic propaganda.

But the reality is terrible enough: neighbour betraying neighbour to the inquisitors; water torture or the rack used on prisoners including 90-year-old women and 13-year-old girls; imprisonment without trial; the gruesome and humiliating public procession known as the “auto da fe”; the hypocrisy that saw inquisitors “relaxing” confirmed heretics to the secular arm for burning at the stake, because as men of God they could not execute anyone themselves.

We now know that far fewer people died as a result of the Spanish Inquisition than was once thought; most people who fell under suspicion would be “reconciled” to the church and released. Over three and a half centuries, around 6,000 people would be executed.

But the truly terrifying thing about inquisitions was the policing of belief in the first place. As one citizen of Toledo wrote in 1538:

Bit by bit many rich people leave the country for foreign realms, in order not to live all their lives in fear and trembling every time an officer of the Inquisition enters their house; for continual fear is a worse death than a sudden demise.

The European “wars of religion” were a series of appallingly bloody conflicts – but were they really about religion?

These conflicts in 16th- and 17th-century Europe are frequently offered as irrefutable evidence that religion in general, and Christianity in particular, leads to division and bloodshed.

In the wake of the Reformation in the early 16th century and the split between the Catholic and Protestant churches, Europe descended into a series of conflicts, some local, some enormous in scope. The most intense was the Thirty Years’ War (1618-1648), which left about 8 million people dead – more than the American Civil War and the Napoleonic Wars combined! Some areas of Europe lost more than two-thirds of their population during the Thirty Years’ War.

However, historians point out that these conflicts are way more complicated than religious squabbles – as shown by frequent alliances between Catholic and Protestant countries or groups, as well as Catholic vs Catholic or Protestant vs Protestant battles. Rather, the so-called “wars of religion” represent the birth-pangs of the modern nation-state – the transition from empires and church rule to sovereign countries. As David Bentley Hart (University of Notre Dame) explains:

These wars, to a very great extent – what they really tell us about modernity is just how much blood was spilled in order to arrive at the modern accommodation of the absolutely sovereign state … They tell us actually that the death of Christendom was violent and convulsive but they don’t tell us about the nature of religion one way or the other.

The Troubles in Northern Ireland saw some very ugly clashes between Catholics and Protestants over thirty years of conflict.

The Troubles (1968-1998) is also often cited as an example of a religious war. And it certainly had a strong sectarian element.

A closer look shows a much more complex picture, in which republicans (who wanted Northern Ireland to leave the UK and join the Republic of Ireland) and loyalists (those who wished to stay) used their ethnic and religious identity as tribal markers – to distinguish “us” and “them” in an intractable political situation. As Rowan Williams explains:

There are plenty of circumstances where for Christians, as indeed for Muslims, religion is a really, really good alibi, a really good banner to march under. If there’s a conflict, that’s basically about something else, it’s terrifically helpful to make it a religious conflict because it reinforces your own righteousness.

“I get sick of getting into a London taxi and there comes a moment when the taxi driver will say, what do I do for a living? And I tell him I write about religion, and then he will intone this sentence, repeating it like a kind of mantra: Religion has been the cause of all the major wars in history. Utter nonsense!”

Karen Armstrong, Author

But what about … secular violence?

Does religion cause all the wars?

The 20th century was the most violent in human history. How does the brutality of atheist regimes stack up against religious violence? And what might that tell us about humanity?

But what about … the Old Testament?

The Bible itself is full of violence. What if God is just like that?

The atheist Richard Dawkins has called the God of the Old Testament “arguably the most unpleasant character in all fiction”: jealous, petty, unforgiving, vindictive, even genocidal. If that’s what God is like, then the worst behaviour of Christians would make perfect sense.

How to judge the church

If Christians have so often departed from the one they claim to follow, why should anyone take what they believe seriously?

It’s easy to write off Christianity because of the many wrongs Christians have done. But maybe that would be like judging a piece of music on the basis of a bad performance …

Playing in tune

Few people have embodied Jesus’ command to “love your enemies” more effectively than a Baptist preacher from the American South: Martin Luther King Jr.

From the time of his emergence as a reluctant leader of the Montgomery bus boycott in 1955, Martin Luther King Jr drew on the teaching of Jesus, the methods of Gandhi, and the resources of faith found in the church to spearhead a powerful movement for civil rights for African-Americans.

In the face of harassment, violence, imprisonment, and character assassination, he advocated a method of strictly non-violent resistance, insisting that he and his fellow activists would resist an evil system, but continue to love the individuals within it.

The famous Selma to Montgomery marches of 1965 – a dramatic, peaceful, but also costly victory for African-American voting rights – demonstrated the force and wisdom of Jesus’ command to turn the other cheek.

Thin vs thick religion

People sometimes think that religions are, by their very nature, violent. And then the obvious conclusion is: the less religion you have, the better off you’re going to be.

Miroslav Volf

It’s clear from history that Christianity has been a force both for peace and for violence.

Perhaps the right question then becomes not so much “Does religion cause war?” as “Under what circumstances does it fan the flames of conflict?”

Yale philosopher Miroslav Volf suggests that religions (including Christianity) will foster violence in situations where they have become thinned out of their essential content and convictions. Instead of acting as a transformative influence on people who identify with it, thin faith becomes a mere tool – co-opted to whatever ends we set for ourselves, including war and violence.

By contrast, thick faith maintains its moral content and has the power to shape an individual or communal vision of the good life in ways that defuse and oppose conflict.

What this means is that, in response to religious violence, maybe what the world needs is not less religion but more religion – of the “thick” kind!

“Generosity toward the other, forgiveness of others, reconciliation … all of that is central to the Christian faith.

Put it to being central in practice and you’ll have a major contribution to a peaceful world.”

Miroslav Volf, Yale University