Pope Francis, in his encyclical Fratelli Tutti, comments upon the use and misuse of the just war tradition within Catholicism (FT 256-62). His main point is that “in recent decades every single war has been ostensibly ‘justified’” by its apologists, when in fact “it is very difficult nowadays to invoke the rational criteria elaborated in earlier centuries to speak of the possibility of a ‘just war” (FT 258). In other words, in the modern era, there are no just wars, but merely the abuse of the just war tradition in attempts to justify war. Francis repeats the call of his predecessor Paul VI to the U.N.: “Never again war!

In a footnote, Francis refers to St. Augustine having “forged a concept of ‘just war’ that we no longer uphold in our own day” (FT 258, note 242). He does not specify exactly what in Augustine’s thought “we” (presumably meaning Catholics) “no longer uphold.” I cannot say for sure what he may have in mind—perhaps he will specify in the future—but I suspect he means Augustine’s core belief that war can be an instrument of justice, by which one nation may punish another for wrongs inflicted. Francis, following the teaching of Pope John XXIII, altogether rejects this as a justification for waging war.

In this post I will outline the main principles of just war theory, then explain how Francis narrows the criterion of just cause by rejecting the legitimacy of modern warfare as an instrument of justice. He suggests that modern weaponry can scarcely fulfill the criterion of proportionality, as the evils unleashed by a war are almost guaranteed to be greater than the injustice it seeks to remedy. As a result, the possibility of a war today being just is virtually ruled out, except as last-resort defense.

Six Criteria for Ius Ad Bellum (Just War)[1]

First of all, it must be noted as a matter of history that Augustine did not formulate a doctrine of “just war” in the sense of a clearly-defined, explicated theory. Rather, he sporadically mentions the justice and injustice of war in various writings spread across his vast corpus, especially in Against Faustus. The first author to approach anything like a theory of just war is Gratian, the celebrated canonist/theologian. His compilation of canon law, the Decretum (ca. 1140), cites Augustine 78 times in the context of just war.[2] The first person to define a theory of just war per se is St. Thomas Aquinas in the Summa Theologiae 2,2,40,1: “In order for a war to be just, three things are necessary.” These are proper authority, just cause, and right intention. For each of these, Aquinas has a clear quotation from Augustine in support, which shows how comments made here and there throughout his corpus became the patristic authority for this medieval theory.

Proper authority means that only a lawful government can carry out a just war. “It is not the business of a private individual to summon together the people” (ST 2,2,40,1). This rules out things like campaigns of personal vengeance, creating private armies, terrorism, or organized crime. Just cause means the nation being attacked must “deserve it on account of some fault” (ibid.), such as having stolen another nation’s property. Right intention means that the nation waging war must do so in order to secure peace and punish the wicked—not for cruelty, vengeance, “the lust of power” (libido dominandi, Augustine’s memorable phrase), or any other vicious motive.

Aquinas’s three criteria, drawn from scattered remarks of Augustine, remain the bedrock of the theory, but no contemporary just-war theorists limit it to only these three factors. This is why it is called the just war tradition: the criteria have expanded and been refined throughout the centuries and are still developing (like all living traditions). In addition to Aquinas’s, three additional criteria are universally recognized: last resort, reasonable chance of success, and proportionality.[3]

Last resort means that war is only acceptable when all peaceful means of obtaining justice have failed; it is the last option when everything else has failed. Reasonable chance of success rules out waging hopeless wars out of a sense of self-righteousness. To go out guns blazing is contrary to Christianity and evil, no matter how often this is eulogized in movies. The reason it is wrong is that it unleashes the evils of war for no good reason. If a war cannot succeed, it consigns people on both sides to death and other miseries without hope of attaining the good that could make it worthwhile. It would be better to simply suffer the evils rather than create more. This leads to the third criterion of proportionality: the evils unleashed by war must not be greater than the evils it seeks to remedy. In other words, the cure must not be worse than the disease. For example, if after 9/11 the U.S. had dropped nuclear bombs on Afghanistan, we would have inflicted far greater evils than the ones we ourselves suffered. That the cause was just would be irrelevant, since all criteria must be fulfilled for a war to be just.

Ius in Bello: Discrimination and Proportionality

The six above criteria are now known as “ius ad bellum” (right to war). If all six criteria are truly fulfilled, then a nation has a moral right to go to war to obtain justice. But just war theory adds two additional criteria for how a nation must behave during war, which are called “ius in bello,” meaning justice during war (ius means both justice and right). The idea that “there are no rules in war” is completely rejected by Catholic tradition. This mindset has been a tremendous source of evils and is foreign to the law of God, which can never be suspended. The two principles are proportionality (again) and discrimination.

We already saw the proportionality criterion; repeating it here means that it must be continuously maintained throughout a war. If it is ever falsified, the war has become unjust. Even in a just war, the righteous belligerent must continually evaluate whether each individual instance of violence is justified proportionally. They must always ask, “Is this particular act of destruction just?” If an act of violence will unleash greater evils than what it seeks to remedy, it is unjust. For example, you could not bomb an entire city just to gain a minor tactical advantage. It is questionable whether any actual war, even if just in its inception and goal, has ever been waged justly in actual fact (the Allied fire-bombing of Dresden, Germany, comes to mind).

Finally, the principle of discrimination forbids the deliberate targeting of non-combatants. Violence must be limited to military targets. It is always likely in war that non-combatants will be incidentally killed as collateral damage. This is only tolerable if it remains proportional (thus the two criteria for ius in bello work in tandem). For example, a military base is a legitimate target, even if some civilians are there. However, targeting a hospital or school at which a large group of soldiers are stationed for security is clearly illegitimate. You also need to consider the scope of the damage. There could be a military target in the middle of a populated city, for example. Unless a precision strike could be carried out, it would be unjust to attack the base, knowing that it would kill large numbers of non-combatants residing in the area. There is no prescribed mathematical ratio, but common sense would indicate that the ratio of non-combatants to combatants would have to be very small. Thus, the presence of some soldiers—even a great number of soldiers—in a city could never justify dropping a nuclear bomb on that city, as the U.S. did twice during World War II.[4]

Modern warfare is not an instrument of justice

The pope, referring to the Catechism of the Catholic Church (2309), gives a much narrower interpretation of just war than Augustine and Aquinas. He specifies that what the Catholic Church considers legitimate is not just war per se, but just defense: “The Catechism of the Catholic Church speaks of the possibility of legitimate defence” (FT 258). The use of italics emphasizes the narrowing of one of the key criteria for just war: just cause.

For both Augustine and Aquinas, war can be a means of obtaining justice and as such may be inflicted in proportion to any grave injustice inflicted against a people. It is a form of punishment, like a fine or jail for individuals. Aquinas does not even mention self-defense as an example of just cause, though obviously it is, but mentions one nation refusing to make amends for wrongs inflicted on another (ST 2,2,40,1). For example, if one nation were to harm another (which nowadays could be done not only with bombs but through cyber warfare, unfair trade practices, economic sanctions, etc.), they could conceivably be attacked in retribution.

Pope Francis entirely rules out this type of thinking: “We can no longer think of war as a solution, because its risks will probably always be greater than its supposed benefits” (FT 258). Although nations still wrong one another in the modern world, the means of justice by which such wrongs may be righted can no longer include war. This completely re-frames the terms in which just war is imagined, which explains why he said that “we no longer uphold” Augustine’s (and Aquinas’s) conception.

In proposing this fundamental shift, the pope draws upon the aforementioned criterion for ius in bello: “At issue is whether the development of nuclear, chemical and biological weapons, and the enormous and growing possibilities offered by new technologies, have granted war an uncontrollable destructive power over great numbers of innocent civilians” (ibid.). Due to the astonishing and horrific destructive power of modern weaponry, proportionality is hard to maintain. Modern warfare unleashes so many grave evils, it is hard to imagine a situation in which it would not be worse than whatever injustice precipitated it. “What might appear as an immediate or practical solution for one part of the world initiates a chain of violent and often latent effects that end up harming the entire planet and opening the way to new and worse wars in the future” (FT 259). I think of the Iraq War, which at first may have seemed justifiable due to false intelligence that Saddam Hussein possessed weapons of mass destruction. Hussein was dead within three weeks, but seventeen years later, the world still suffers ongoing effects that will last for decades to come. No one can seriously doubt that Pope Francis’s teachings in this encyclical were informed by the calamity of the wars in Iraq and Afghanistan.

Despite the false narrative that Pope Francis keeps breaking with Catholic tradition, here—as always—he grounds himself in the Church’s tradition and Magisterium, especially the Second Vatican Council and Pope St. John XXIII. The questioning of war as a means of justice was already made by John XXIII, whom Francis quotes: “it no longer makes sense to maintain that war is a fit instrument with which to repair the violation of justice” (FT 260, quoting Pacem in Terris 127). For John XXIII, this was due to nuclear weapons, but Francis adds chemical and biological weapons. Just war theory was first formulated in the Middle Ages, when soldiers lined up on battlefields and attacked each other with swords and shields, the ill effects of which—bad as they were—were more easily contained than those of nuclear, chemical, and biological weapons.

In the Middle Ages, the Crusades were considered “just” due to the perceived injustices of the Islamic empire. Also deemed “just” were crusades against heretics like the Albigensians, whose false doctrines were considered a capital offense. With the Second Vatican Council, the Catholic Church has irrevocably and definitively closed the door on religiously-motivated violence. “Violence has no basis in our fundamental religious convictions, but only in their distortion” (FT 282). Beyond legitimate defense, any use of Catholic doctrine to justify violence is ipso facto a distortion.

Responsibility to Protect?

Many people today argue that the international community should intervene—militarily, if necessary—when there are grave abuses of human rights. This is called the “responsibility to protect” (R2P). The Vatican has endorsed this policy, but without condoning military intervention. The most recent, relevant example of this principle is Bashar al-Assad’s use of chemical weapons against his own people. Many people, including U.S. Democrats, praised Donald Trump for launching, in coordination with allies, air strikes against Syrian targets on April 14, 2018. Pope Francis, however, opposed this and asked people to pray for peace. This demonstrates the extent to which he opposes virtually any use of violence, even in the face of human rights abuses. However, the issue of R2P and violence is not directly addressed in Fratelli Tutti. Insofar as it falls in the category of “legitimate defense,” it remains an open question about which Catholics may disagree in good faith.

The end of just war theory?

Is this the end of the just war tradition in the Catholic Church? I don’t think so, but it is a radical narrowing of it in line with the words and deeds of his predecessors. As we saw, John XXIII said in a papal encyclical that nuclear war cannot be an instrument of justice, and Paul VI took that message to the U.N. to declare “Never again war!” John Paul II apologized for the Crusades and tried to persuade the Bush administration against invading Iraq. As with the death penalty (FT 263-70), the Catholic Church, under the leadership of its Sovereign Pontiffs, now unequivocally places itself on the side of peace, life, and mercy.

Nevertheless, Francis has kept the door open, at least in theory, for “legitimate defense.” When one nation attacks another, just as when one individual attacks another, it is within the law of God to defend oneself, even by lethal force if necessary, so long as your intended goal is to stop the aggressor rather than to kill them per se. Within this narrow scope, the criteria of just war theory should still be applied. Even legitimate defense must be limited by proportionality, discrimination, last resort, and the rest of the just-war criteria.

I could imagine this coming into play, hypothetically, if one nation were to launch a sneak-attack invasion. Even then the invaded country should give careful thought to the criterion of last resort and whether the invasion could be stopped by non-violent means, such as by appealing to the intervention of the international community. In Fratelli Tutti, Francis discusses the Charter of the United Nations as an “obligatory reference point of justice” in today’s world (FT 257). But barring such unlikely hypotheticals, it is hard for me to see how any unilateral military action, even if ostensibly done in self-defense, could fulfill all the criteria for justice as proposed by Pope Francis.

The bottom line is clear: war is evil (indeed, Aquinas treats it alongside other vices, such as hatred, sloth, envy, and schism). We should not attempt to justify it “by invoking all sorts of allegedly humanitarian, defensive or precautionary excuses” (FT 258). Rather, we must recognize the harsh reality that “every war leaves our world worse than it was before. War is a failure of politics and of humanity” (FT 261). Instead of getting entangled in “theoretical discussions,” the pope urges Christians to “touch the wounded flesh of the victims” (ibid). Or perhaps we should just say: “Blessed are the peacemakers, for they will be called children of God” (Matt 5:9).


[1] Ius (pronounced “yoos”) is the Latin word for right, law, and justice, and is often spelled in the medieval fashion as jus. Ius ad bellum means, basically, “right to war” or, more loosely “just war.”

[2] Phillip Wynn, Augustine on War and Military Service (2013), 9.

[3] See, for example, Alexander Moseley, “Just War Theory,” in the Internet Encyclopedia of Philosophy. These criteria can be found in any number of works on the subject.

[4] Defenders of the nuclear bombs usually cite the quick ending of the war saving many lives, but that is an “ends justify the means” argument that is definitively rejected by Catholic moral doctrine (CCC 1753, 59).

Image: Dresden 1945. By Bundesarchiv, Bild 183-Z0309-310 / G. Beyer / CC-BY-SA 3.0, CC BY-SA 3.0 de, https://commons.wikimedia.org/w/index.php?curid=5371503

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Dr. Rasmussen is an adjunct professor in Georgetown University's Department of Theology & Religious Studies. He has a Ph.D. in the same subject from The Catholic University of America, specializing in historical theology and early Christianity. He is the author of Genesis and Cosmos: Basil and Origen on Genesis 1 and Cosmology (Bible in Ancient Christianity 14; Brill, 2019).

Pope Francis and Just War Tradition
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