Last July Pope Francis spoke about the hundredth anniversary of World War I to a crowd gathered for the Angelus in St. Peter’s Square. He used the occasion to exhort his listeners to abolish war: “Never war! Never war! I think most of all about children, whose hopes for a dignified life, a future, are dashed, dead children, wounded children, mutilated children, orphans, children who have the leftovers of war for toys, children who don’t know how to smile. Stop it, please! I beg you with all my heart! It’s time to stop!”

But the pope has since suggested that military action to protect civilians from massacre at the hands of groups such as the Islamic State can be just. This tension—between calls to abolish war and cautious support for the use of armed force to protect the vulnerable from violence—is nothing new at the Vatican. In 1991, St. John Paul II wrote, “No, never again war” and called on humanity to “proceed resolutely toward outlawing war completely,” but the same year he also said, “We are not pacifists, we do not want peace at any cost.”

So what’s going on here? Does contemporary Catholic teaching reject war or not? The answer is yes and no. The church still deems military action to be permissible in certain narrow circumstances, while simultaneously urging us to work for a world in which war is never necessary, and insisting that such a world is possible. In other words, church teaching is not pacifist, but it is abolitionist.

This formula finds its clearest expression in Vatican II’s Gaudium et spes, which acknowledged that “governments cannot be denied the right to legitimate defense once every means of peaceful settlement has been exhausted,” but only until war is “rooted out of human affairs.” The document demanded that human beings “free ourselves from the age-old slavery of war” by moving toward “the time when all war can be completely outlawed by international consent” through “the establishment of some universal public authority” that provides a better way to uphold international peace, security, and justice.

Here the development of Catholic teaching on war resembles the development of its teaching on capital punishment. The Catholic tradition once accepted the death penalty as a normal and just method of criminal justice but now advocates its abolition, not because it is never permissible in theory, but because we now have effective alternatives. Capital punishment is a cruel and violent practice, and now that it isn’t necessary to ensure public safety, it no longer has a legitimate place in a civilized society. Catholic teaching has the same vision for warfare: it is a cruel and violent practice that the world can and should find ways to do without.

Many people, of course, consider calls to abolish war utopian and dangerous. Images from war zones around the globe make the idea sound ridiculous. It is hard not to see war as an unavoidable part of the human condition. As Albert Einstein put it, “So long as there are men, there will be wars.” War also seems necessary, at least in some circumstances, to protect innocent people and uphold a peaceful and just order in the face of those who are willing to use war for destructive and unjust ends. For many, the call to give up war amounts to a form of reckless unilateral disarmament.

So is the conventional wisdom correct? Is the Catholic Church hopelessly unrealistic in its demand that humanity abolish war? I don’t think so, for two reasons.

The first is historical precedent. In calling for an end to war in Centesimus annus, John Paul II drew a parallel to how “a system of private vendetta and reprisal has given way to the rule of law.” It is a telling example. We take modern policing and courts for granted, but these are relatively recent institutions. For much of human history, people turned to private acts of vengeance and duels as a matter of course. These practices were considered unavoidable, a reflection of the natural human tendency to give and respond to offense. They were the only way to protect oneself and one’s family from unjustified attack. An early governor of South Carolina, Lyde Wilson, argued that war and dueling were based on the same thing: “the first law of nature, self-preservation.” Not surprisingly, those who urged the abolition of private vengeance and dueling were dismissed as foolishly utopian, and even as dangerous for seeking to dismantle institutions necessary to punish wrongdoing and vindicate the innocent. Yet today it is hard for most of us to imagine that these violent practices were once part of everyday life.

Or, again, consider capital punishment. Through most of recorded history, societies around the world executed people for things we now consider either relatively minor crimes or no crime at all—poaching, picking pockets, stealing horses, adultery, heresy. The death penalty was routine, pervasive, and accepted as just the way the world worked. And it was justified in terms remarkably similar to those used to justify war: it was perhaps an unpleasant form of violence, but it was necessary to uphold a just and peaceful order and to protect the innocent. Movements to abolish the death penalty are a relatively recent phenomenon, and the abolitionists were initially accused of sentimentality, ignoring the reality of evil in the world, and threatening to turn society over to blood-thirsty criminals. Yet over the course of the past century, most countries have abolished capital punishment, and the handful that have kept it, including the United States, have dramatically curtailed its frequency.

Perhaps the most powerful historical precedent for abolishing war is chattel slavery. Like war, slavery first appeared about twelve thousand years ago. And like war, it quickly spread to every major society and region of the world. Over its long history, it was simply accepted as an inevitable part of the human condition. Indeed, it is striking how just-war theorists from Augustine to Aquinas to Francisco Suárez used the same language to justify slavery that they used to justify war, defending it as a necessary part of a fallen world marked by sin. As slavery took on an explicitly racial character later in its history, its defenders considered it essential to the natural racial order that protected superior peoples from the savagery of inferior ones. In words that many today might apply to war, one eighteenth-century English commentator, Edward Bancroft, wrote of slavery, “Many things which are repugnant to humanity may be excused on account of their necessity for self-preservation.” It was only within the last century of its long history that a sustained movement to abolish slavery arose. These early abolitionists were condemned as recklessly naïve for challenging something so deeply rooted in human history and fundamental to social order, yet their movement rapidly produced one of the world’s great moral triumphs.

As these examples show, it is possible to abolish longstanding and widespread violent practices once accepted as natural and necessary parts of the human condition. Each gradually disappeared as social attitudes shifted, political actors moved to suppress them, and new institutions arose as alternatives. And such shifts are realistic because they do not require a world of pure peace, love, and understanding. Abolishing vendettas and duels did not eliminate grudges and interpersonal violence. Nations that have gotten rid of capital punishment may still have plenty of other injustices in their criminal-justice systems. And ending chattel slavery certainly did not eliminate other forms of exploitation or racism. One of the strengths of Catholic social teaching is its recognition that progress does not require perfection. The reality of sin in the world and the strife it brings does not prevent constructing, in the words of Gaudium et spes, “a world more genuinely human.” Realism about human flaws is no barrier to gradual and partial but nonetheless genuine social reform. It does not negate what John Paul II called Catholicism’s “optimistic view of history.”

MIGHT WAR FOLLOW the same path to extinction? What we know about war suggests it could, and this is the other reason not to dismiss the church’s call for its abolition. In urging humanity to rid itself of war, contemporary Catholic teaching emphasizes a powerful set of tools for global peacemaking. First, removing the roots of war means working to alleviate poverty and inequality, protect human rights, and promote democracy and the rule of law. Second, while conflicts among and within countries will persist, it is possible to resolve these through nonviolent negotiation and mediation. Third, areas experiencing chronic conflict require robust international peacekeeping commitments to break local cycles of warfare. Fourth, rather than military force, the community of nations can rely on a mix of diplomacy, sanctions, and incentives to pressure its members to uphold international norms. Fifth, for people facing oppression, methods of nonviolent direct action continue to spread around the world as effective alternatives to armed struggle.

These tools all rely on more effective international cooperation and coordination. This is why popes since Vatican II have stressed the importance of greater global governance, what Benedict XVI in Caritas in veritate called a “true world political authority” able to “ensure security for all, regard for justice, and respect for rights.” Rather than concentrated in some remote seat of power, such authority would be spread across an interlocking web of global institutions—international laws, treaties and their enforcement regimes, non-governmental organizations, United Nations agencies, civil-society groups—that Catholic teaching consistently commends.

Some critics dismiss the church’s peacemaking commitments as more unrealistic sentimentality. George Weigel, for example, has described faith in greater international governance and multilateral cooperation as “inexplicably stupid” and lamented that this “fantasy” continues to appear in papal encyclicals. But it is remarkable how much social-scientific research on armed conflict supports the effectiveness of the very tools Catholic teaching emphasizes. Those who study trends in warfare find that greater economic development, more participation in international trade, and deeper involvement in regional intergovernmental bodies all significantly reduce a country’s risk of war. So too does democracy, the rule of law, and effective governance. The research also shows that there is much that the international community can do to promote these economic and political trends in countries most at risk of war. The use of mediation and peace agreements to resolve disputes between and within countries has been increasingly effective. Meanwhile, international peacekeeping missions and peace-and-reconciliation initiatives have significantly reduced the risk of conflict breaking out again in places where it has recently ended. Those who study armed conflict have also shown the effectiveness of diplomacy and sanctions in influencing state behavior without resort to war. Finally, studies show that in the past century nonviolent civil resistance has been twice as effective as armed struggle against both domestic dictators and foreign oppressors—and this effectiveness gap has grown even greater in the past few decades. The church’s ideas about peacemaking turn out to be pretty realistic after all.

The best news from research on armed conflict is how infrequent it has become. War still exists, of course, as news accounts from Syria and Ukraine remind us every day, but there has been a gradual long-term decline in war across the past several centuries, one that has dramatically accelerated in the past sixty years. Whether measured by the number of active wars or the number of battle deaths per capita, we may be living in the most peaceful period in human history. Wars between states, especially those between great powers, have virtually disappeared. In many parts of the world, countries still have disputes but don’t even consider using war to resolve them. The Greek debt crisis, for example, sparked serious conflict within the European Union, but nobody thought Germany was going to invade Greece, even though collecting national debts was once a common reason for war. The thought of the United States going to war in order to resolve various differences with Canada or Mexico over trade or pollution or drug trafficking is now as improbable as the thought of two doctors in Peoria fighting a duel over a medical-ethics complaint.

Today’s wars are almost all civil wars fought within impoverished, frail, or failed states. There is no reason to think that the tools of peacemaking emphasized by Catholic social teaching cannot be effectively used to bring such states into existing zones of peace, where war is simply no longer considered a valid option.

There is obviously no guarantee that the decline of war will continue or that humanity can push this decline so far as to abolish war completely. Even if we did manage to eliminate warfare, there will still be plenty of political violence, injustice, and general human misery around the world. But it is clear that Catholicism’s call to abolish war, like its call to abolish the death penalty, is far from foolish.