“Never again war!” It has become a mantra for popes over the last five decades, one signaling the emergence of Catholic teaching as a remarkably powerful voice against warfare in the contemporary world. The church’s case against war combines a sweeping critique of war’s nature and a detailed vision for abolishing it by strengthening its alternatives and actively building peace. This case amounts to, in the words of John Paul II, a comprehensive and urgent “No to War!”
The church has not always been such a strong critic of war. While the earliest Christians usually rejected participation in warfare as contrary to the Gospel, starting in the fourth century thinkers such as Ambrose and Augustine gradually laid the foundations of the Christian just war tradition. Developed over the centuries since, this tradition argues that war, while often terrible, is sometimes necessary to protect a just and peaceful order given the realities of sin in the world. Under certain conditions—a just cause, right intention, last resort, and others—going to war is morally legitimate. And fighting such wars once underway can be morally just too, as long as participants observe certain moral limits—not intentionally attacking civilians, avoiding disproportionate destruction, treating prisoners humanely, and others. This was the dominant lens the Catholic Church used to analyze war for most of its history up into the twentieth century. Not all wars are just, but some are, and war itself, while regrettable, is a normal and often legitimate part of the way countries behave in the world.
Beginning in the twentieth century, however, Catholic teaching on war and peace underwent significant shifts, especially after Vatican II’s promise to “undertake an evaluation of war with an entirely new attitude.” While its interpretation of the just war tradition was once flexible enough to accommodate war as a normal part of statecraft, the Vatican increasingly applied stricter interpretations, using them to condemn wars for such things as lacking just cause or right intention, ignoring alternatives demanded by the last resort requirement, unleashing disproportionate destruction on societies, and, especially, indiscriminately killing civilians. Rather than emphasizing war’s necessity in protecting a just and peaceful order, Catholic teaching’s emerging case against war condemned it as a threat to such an order, creating cycles of violence, devastation, and oppression that only made things worse. Alongside these growing condemnations of war and, eventually, calls to abolish it completely, the church emphasized alternatives to armed conflict such as negotiation, mediation, and nonviolent resistance. It urged the world to address the roots of war through greater global cooperation, international law, and a commitment to sustainable economic development, human rights, and democratic political institutions. In this way, the Vatican increasingly emphasized principles associated with what is often now called a “just peace” perspective.
While this shift to a much more critical view of war has been dramatic, there remains the question of whether Catholic teaching still allows any space for a just war under certain conditions. On the yes side, even as Vatican statements increasingly condemned war, they allowed for narrow exceptions as a last resort—either in national self-defense or as military interventions to prevent humanitarian disasters such as genocide—at least until humanity succeeds in ending war itself. Vatican II’s Gaudium et Spes states: “As long as the danger of war remains and there is no competent and sufficiently powerful authority at the international level, governments cannot be denied the right to legitimate defense once every means of peaceful settlement has been exhausted.” And John Paul II, who once said “we are not pacifists,” gives a qualified endorsement to “humanitarian interventions” to disarm an “unjust aggressor” when other means to prevent grave abuse of innocent populations have failed. More recently, however, church teaching may have closed this remaining space for morally-permitted war. While pointing to the need to resist “unjust aggression,” Francis states, “I don’t say bomb, make war,” and calls the decision “to engage in war” a “mistaken understanding of our own principles.” In 2020’s Fratelli Tutti, Francis warns, “War can easily be chosen by invoking all sorts of allegedly humanitarian, defensive or precautionary excuses….In recent decades, every single war has been ostensibly ‘justified.’” The nature of modern warfare makes it “very difficult” to ever satisfy traditional just war criteria and therefore to even “speak of the possibility of a ‘just war’” today. According to Francis, Augustine “forged a concept of ‘just war’ that we no longer uphold in our own day.” And in statements addressing the war following Russia’s 2022 invasion of Ukraine, Francis is even more direct, saying “wars are always unjust” and “there is no such thing as a just war: they do not exist!”
There have, then, been major and, given the church’s millennia-long existence, relatively recent developments in Catholic teaching on war and peace over the last century, ones rooted in shifts in both how the church views the world and how it communicates the nonviolent teachings of Jesus in the gospels. And these developments are ongoing. This means it is an area of teaching that is still relatively fluid, and therefore one necessarily marked by a number of ambiguities and unanswered questions, especially around if and when armed force is ever morally permitted. Until we have a major authoritative document, such as a papal encyclical, that directly addresses the question in detail, those who believe Catholic teaching permits some instances of armed force, either in self-defense or to protect vulnerable populations from mass atrocities such as genocide, can certainly find support for their position, just as those who believe the church no longer permits such force can find support for theirs.
(excerpted from the introduction)
