Why Just War Theory Isn’t Enough

What is the correct sensibility that a Christian ought to cultivate with regard to war? I regard this as one of the most urgent moral and spiritual questions of our age. All too often, when a new armed conflict breaks out in the world, Catholic commentators are quick to analyze it in terms of the criteria of just war theory, originating from St. Augustine.

I do not for one moment deny the importance of just war theory and its venerable tradition of thought, which continue to provide much guidance for Christians and others of good will. But just war theory may not be enough, if it lacks a fine-grained awareness of either new and emerging ways of resolving conflict or of the complex financial and political interests involved in decisions to go to war. For such reasons, Pope Leo XIV has called just war theory “outdated” (Magnifica Humanitas §§192-93). Warfare in the modern world is not often reducible to aggression and self-defense, and moral reflection needs to cultivate a new sensitivity towards what lies behind the violence of war. For there is a risk that, in beginning our reflection on war with just war theory, we become too quick to excuse as “just” what may at heart be purely cynical and self-serving politics. We therefore dull our sensitivity towards the fundamental senselessness of war—a senselessness which the French mathematician and philosopher Blaise Pascal puts across so vividly in his celebrated Pensées, and which we need to recover:

Could there be anything more absurd than that a man has the right to kill me because he lives on the other side of the water, and his prince has picked a quarrel with mine, though I have none with him?[1]

Beyond “Just War”

It is helpful to start with some clarity about what just war theory is and what it is not. What we must recognize, first of all, is that whenever the Church offers some systematic set of moral criteria for our consideration—just war theory, the doctrine of double effect, ordinary vs. extraordinary means—these are highly compressed moral insights, crystallized and refined through centuries of debate and real-life experience of good and evil. They are a kind of shorthand, especially for those who need to make important decisions quickly, but they do not function as a decision-making machine, nor do they replace the need for moral thinking and the formation of our consciences. They are only as useful as our appreciation of the moral fundaments on which they rest.

To take an analogy from Catholic bioethics, we cannot hope to understand the distinction between ordinary and extraordinary means in relation to medical treatment unless we first have an appreciation of the intrinsic dignity of human life, which is a gift from God, of which we are all stewards. We cannot hope to understand why medical treatment in some contexts becomes disproportionate (i.e. extraordinary means) and thus can be refused or withdrawn, unless we develop a sensibility along the following lines: that treatment must serve the whole human person and not just the narrow symptom or disease, and that human life on this earth, while intrinsically valuable, is subordinate to a still greater good, which is eternal life with God.

Similarly, just war theory must not begin from a false equivalence that sees war as sometimes just, sometimes unjust. It begins with the presumption that the destruction of human life is an offense against God. Nowhere is this clearer than in the Catechism of the Catholic Church, where the criteria for just war are placed within a section entitled “Safeguarding Peace,” and which begins with a restatement of the Fifth Commandment prohibiting murder (§§2302–2317). Additionally, just war theory in the Catholic tradition carries with it the presupposition that something has already gone wrong—some aggression has already begun or is imminent and not preventable by other means. So, there has already been a failure on the part of all parties involved; after all, wars do not break out from nowhere, but reflect underlying political struggles and goals. Military action can be taken in legitimate defense to contain evil, but since it invariably destroys human life, it does not lose its character as a sorrowful duty, borne of prior human failure and weakness.

One might even go so far to say that “just war theory” is something of a misnomer, for it implies that both aggressor and defender are essentially pursuing the same kind of action, viz. “war,” although only one does so justly. In the Catholic moral tradition, it is well-established that when a starving person takes a loaf of bread from a shop because it is his only way to survive, he is not performing a “just theft”; it is simply not theft. In language that resembles the criteria for just war, Aquinas says that when someone is “in some imminent danger, and there is no other possible remedy” then he may aid himself by means of someone else’s property such as food or shelter, and this would not even be “properly speaking theft or robbery.” Regarding the status of any such “stolen” property, Aquinas affirms that “need has made it common” (Summa theologiae II-II, q. 66, a. 7). The moral structure of the starving person’s act—constituted by both the circumstances and the intention alongside the physical nature of the act (which outwardly resembles ordinary theft)—is thus completely different from plain shoplifting. Furthermore, the prior existence of injustice is itself something we must bewail as Christians, and the desperate act of “theft” while justified may well have injured someone else, viz. the rightful owner, even if in a relatively minor way.

It is therefore important to maintain that legitimate defensive military action, which may employ methods that outwardly resemble some (but not all) of those used by the aggressor, has a different moral character. My insistence on this difference is not motivated by a need for theoretical purity; it is deeply practical. The one pursuing legitimate defense must be clear he is not carrying out the same kind of action as the aggressor, precisely because he is now exposed to a risk inherent in war, which is that the defender might end up becoming more and more like the aggressor. Mission creep in warfare is real; climbdowns and retreats are politically difficult; the oppressed can become oppressors themselves. For combatants and civilians alike, if we focus too much on the similarities between legitimate defense and aggressive war, we also risk replacing our instinctive sense of the pity of war with sentiments of bellicosity, hatred, and vengeance. The damage that war causes is real and is not erased by a just cause; nor does just military action ever fully correct the prior injustice and failures that led to it. These must be resolved politically and peacefully for peace to be just and lasting, and this goes beyond the scope of just war theory traditionally conceived.

What this means for a Christian sensibility towards war is that war is never something to be celebrated, nor something to be pursued in a fit of self-righteousness to rid the world of evils. Simply being up against a regime which has moral shortcomings does not license all hell and fury. To put things in a more precise manner, in legitimate defense the cause of a war may be just and so its outcome of containing evil, if successful, may be rightfully celebrated; its methods, if employed proportionately, are merely tolerated as a means for achieving the good; the fact of human life destroyed by war on any side, civilian or combatant, is always a tragedy, for the opportunity for repentance and virtue has been cut short. This is certainly so in God’s eyes, and it should be in ours: “Have I any pleasure in the death of the wicked, says the Lord God, and not rather that he should turn from his way and live?” (Ezek 18:23).

Furthermore, while the age-old wisdom stands true, that in the Gospels Christ never told the Centurion or any other soldiers to give up soldiering, indicating that soldering is not inherently sinful, it is also important to emphasize that Christ did not unduly elevate soldiering. Instead, he preached, “Blessed are the peacemakers, for they shall be called sons of God” (Matt 5:9), entrusting Christians with a higher calling. On the night of his betrayal in the Garden of Gethsemane, Christ gave us a stark warning of the senselessness of war: “Put your sword back in its place; for all who take the sword will perish by the sword” (Matt 26:52).

War As a Tragedy of Reason

At this point, it may be objected that, by calling legitimate military action not only “sorrowful” but “senseless,” I am being disrespectful to the brave men and women who are willing to defend their homelands with their lives, and who make very real and often painful sacrifices for the sake of the security of others. Yet, is it not the case that those who have seen real armed conflict are often the first to speak out against new wars and to instill in their listeners something of the senselessness of war?

We also owe it to our brave soldiers to be honest about when governments cynically invoke patriotism and the old romance of the supreme sacrifice of dying for one’s country, in their pursuit of dubious ends or downright immoral goals. Recalling the words I quoted from Pascal earlier, much of warfare has to do with quarrels between the princes of the world, and not between the actual peoples of different lands. The tragedy is that these warring princes are often able to mobilize their peoples for conflicts that they do not want, and this is the source of much senselessness in war.

As the eminent British military historian Sir Michael Howard once observed of the Cold War:

War is now seen as being a matter for governments and not for peoples: an affair of mutual destruction inflicted at remote distances by technological specialists operating according to the arcane calculations of strategic analysts.[2]

Remarking on this observation, Peter Hennessy notes that the Cold War reversed the trend of wars growing from conflicts between professional armies into conflicts involving whole peoples and societies, a trend which culminated into the two world wars of the last century.[3] Perhaps this explains the unique moral clarity associated in particular with the victory of the Second World War, seldom to be found in other conflicts of the modern era, which have been the battleground of specialists.

Soldiers are thus made to fight for potentially obscure and non-transparent interests that may not truly serve the common good. Furthermore, with this mindset of arcane calculation, modern warfare with its technological prowess is treated not as a last resort but as a “natural extension of politics,”[4] a regular instrument rather than an extraordinary moral reality. In quoting Pascal at the beginning of the essay, I signal also broad agreement with his pessimism about the limits of applying reason to domains outside of mathematics and science. Even if we leave aside the worry of vested interests and dubious political aims, we can still question whether the specialists’ war betrays an overconfidence in human reason to plan and achieve outcomes in geopolitics surgically. In the end, war in the modern age is a tragedy of reason because it involves a threefold senselessness.

1) First of all, billions of dollars are spent by governments around the world planning for wars that will never happen. I am not questioning the legitimate need for real deterrence; but accepting the need for some deterrence is compatible with recognizing how, as a matter of fact, the massive expenditure on deterrence also perpetuates in no small measure the burning injustice that many in the world continue to die of hunger and have no basic shelter, while weapons that will never be fired continue to gobble up resources that would feed millions. To recall Aquinas on our resources, “need has made it common,” and we have utterly failed those in need.

2) Secondly, the “arcane calculations” of specialists, however precise, are never more than a partial representation of a chess game with more squares and players than can be imagined. However much analysts try to change or restore the “balance of power” and to wargame likely responses to threats and dilemmas, these efforts often prove impotent in actually preventing wars or predicting the actions of another state. War planning, like economic modelling, tends to presuppose that all agents are rational, when we know the reverse is often more likely.

Assuming rational agency helps to limit possible outcomes, which is useful for planning; modelling irrationality is an impossible task because irrationality is the rejection of parameters of thought. How should we know when leaders might suddenly succumb to a strategic miscalculation, whether due to arrogance or eccentricity? Authoritarian leaders, for example, are known to prefer reading raw, unprocessed intelligence to trusting the analysis of experts—Stalin being a prime but not isolated example.[5] It is but one example of radical uncertainty in war planning.

3) Finally, when war itself breaks out, we find that the behavior of militaries and their leaders under pressure—be it political pressure, shortage of resources, or problems of morale—do not always resemble prior assumptions. Faced with this reality, war planners during a real conflict have the unenviable task of trying to project rational order onto a mess of skirmishes and battles. Front lines shift back and forth, key positions are taken and retaken, and in the end millions of lives are lost for little or no discernible advantage in war, due to decisions that were not altogether rational.

So, it is one thing to praise the sacrifices of brave men and women in uniform, but another to see through the folly of much planning and execution of war efforts. A Christian sensibility should take care to cultivate a healthy skepticism about the stated aims of war in the political domain, and the “arcane calculations” that supposedly underpin them. States must continue to plan for their defense, but they should do so with epistemic humility.

For the rest of us, it is important to keep a distance from an unhealthy fascination with the means of war and the analysis of its conduct. There is no shortage of expert analysis on battle lines, strategic planning, and wargames, and these scratch a very particular “geeky” itch. But we must put the wisdom of the world in its appropriate place, namely that it is folly even compared with the foolishness of God (1 Cor 3:19). We must approach war with something like the mentality with which we approach amputation in medicine: we recognize that as a last resort it may needed, and we want someone with the appropriate training and skill to conduct it, someone who is even intellectually animated by it, but we do not want a doctor with an unhealthy fascination for amputation. We want someone who works in concert with others for rehabilitation after the traumatic blow.

Modern Warfare and Proportionality

Finally, a word must be said about the unique abilities of modern technology in warfare to inflict untold damage on humanity. We do not have to come close to the madness of nuclear weapons for this reflection. In one of Pope Leo XIV’s many statements on war in the first quarter of 2026 alone, he said, “After the tragic experiences of the twentieth century, aerial bombardment should have been banished forever!” Let us not get into the parlor game of trying to “clarify” this statement in relation to the Church’s moral teaching on war—it is not a statement of doctrine but something more important: a prophetic word.

Compared with ground forces and naval power, air power is relatively young, but we have a century of experience to look back on. The reality of air power is that its attraction lies not primarily in its ability to destroy specific targets but in its ability to “achieve psychological effect . . . through coercion.”[6] Whether used against civilian populations, political or military leadership, or in support of ground troops, the purpose of air power, put bluntly, is to terrorize, to induce shock and awe. In the Second World War, both the Axis and the Allied powers were guilty of bombing civilian populations, and populations were indeed terrorized, even if their morale and their resolve were sometimes burnished rather than diminished. While bombing civilians is forbidden by international law, the temptation to do so remains strong—with “collateral damage” invoked too liberally. And even putting that to one side, air power remains disproportionately seductive. As Robert A. Pape points out:

For more than a decade, advocates of precision air weapons have argued that wars can be won by selectively taking out an enemy’s leaders, its communication systems, and the economic infrastructure of its major cities. . . . [Air power] promises to win wars in just days, with few casualties among friendly forces and enemy civilians; and it delays committing large numbers of ground troops until they can be welcomed as liberators rather than as conquerors. But decapitation strategies have never been effective, and the advent of precision air weaponry has not made them any more so.[7]

Although the Catechism does not mention air power by name, it seems likely to be a key consideration in the gloss it gives on the criterion of proportionality for just war: “The use of arms must not produce evils and disorders graver than the evil to be eliminated. The power of modern means of destruction weighs very heavily in evaluating this condition” (§2309).

So as a thought experiment, let us assume for the sake of argument that all U.S. military interventions in the Middle East after 9/11 and until the withdrawal from Afghanistan in 2021 fulfilled all the other criteria for just war besides proportionality: the aggressor will inflict grave damage if not stopped; all other means of securing peace have been exhausted; there must be serious prospect of success in using military action. Knowing what we know now, would we say that U.S. military intervention was proportionate? What role did air power, including both planes and drones, play in the terrorizing of civilian populations whether as direct or indirect targets? How many communities have been irrevocably damaged and how many more lives have been lost, which dwarf the number killed on 9/11? How much hatred has war stirred, how much has it strengthened the resolve of civilians to destroy and to take revenge against the West rather than meekly surrender?

I suggest that a Christian sensibility about war must prefer a very strict and rigorous interpretation of the criterion of proportionality, which on many occasions should give leaders pause for thought, even if military action appears just on all other counts.

***

I put it to all Christians and others of good will that just war theory is not enough. Notwithstanding St. Augustine’s legitimate contributions to this legitimate subject, it has to be said that just war theory arose out of specific political contexts, in which St. Augustine was right to consider whether Christians could be justified in taking up arms. But in the earlier Church Fathers there is a predominant strand of pacifism, most notably from Tertullian but also St. Irenaeus and St. Cyprian. To take one of many examples of this strand, Tertullian in his Apology writes: “If we are enjoined, then, to love our enemies, as I have remarked above, whom have we to hate? If injured, we are forbidden to retaliate, lest we become as bad ourselves: who can suffer injury at our hands?”[8] Rather than treat this early pacifism as an aberration which St. Augustine corrected, it is time to reconsider it as a potent source of moral reflection that can correct the excesses of just war theorizing, and give us a new moral clarity regarding the cycle of violence in today’s world. We do not have to be pacifists to elevate peace over war, but we must be serious about not becoming “as bad ourselves,” which means rooting out vested interests that conspire to make war look inevitable.

In Scripture also we see a tension in the Old Testament between the violence of Israel alongside that of its neighbors, and God who says to David, “You have shed much blood and have waged great wars; you shall not build a house to my name, because you have shed so much blood before me upon the earth. Behold, a son shall be born to you; he shall be a man of peace. . . . He shall build a house for my name” (1 Chr 22:8-10). The wars of Israel in the Old Testament are to be acknowledged, but they are not a guide for how Christians should conduct themselves. They are remnants of a different age, when God chose to accomplish his will by working slowly with and through the messy and brutal imperfections of his chosen people, while also calling them to a higher standard of peace and harmony with other nations, which Christ’s revelation confirms.

In our day, we must pay attention to the signs of the times, and recognize what is of the old world and is passing away, and what is our new and higher calling as Christians. Are we worthy of calling Christ the “King of Peace,” if we do not lay down our weapons, and recognize that we are all brothers and sisters?[9] If we have not purged our hearts of an unhealthy fascination with war and violence, if we have not ceased to cheer those who promote violence and vengeance in the name of God, even if we ourselves are not armed? Just as Christ tells us we can sin in our hearts without committing adultery, so it is with war.

Drawing inspiration from Christ (Matt 19:8), we might say, “For your hardness of heart Augustine allowed you just war, but from the beginning it was not so.” Let us bring to bear our most rigorous philosophical and political reflection when considering how we can achieve and maintain a just peace through means other than deterrence and conflict. Let us go beyond just war theory and seek a theology of peace.

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