Assessing the Trump Administration’s Response to the Catholic Church
The “just war doctrine” has unexpectedly emerged as a point of contention in American political discourse. Speaking at a Turning Point USA event on April 14, Vice President J.D. Vance invoked what he characterized as the “more than 1000-year tradition of just war theory,” while criticizing Pope Leo XIV’s condemnation of war. According to Vance, who is a fairly recent convert to Catholicism, they may disagree over whether the conflict is just, but “it’s very, very important for the Pope to be careful when he talks about matters of theology.” House Speaker Mike Johnson soon followed, supporting the criticism of the Pope and telling reporters, “There’s something called the just war doctrine.”
Those remarks followed President Donald Trump’s criticism of the Pontiff as “WEAK on Crime, and terrible for Foreign Policy,” and his Truth Social post featuring an AI-generated image of himself in a Christ-like manner. Secretary of Defense Hegseth has also been criticized for framing military action in overtly Christian terms. Last Thursday, speaking in Cameroon, the Pope warned, “Woe to those who manipulate religion for military or political gain.”
Whatever one’s views on Vance’s and Johnson’s criticism of the Pope, the President’s rhetoric and meme-making, or the Secretary of Defense’s claims of divine mandate, the exchanges have drawn attention to a moral and intellectual framework developed over centuries of Christian thought, with an impact far beyond it. That framework asks when is the resort to war morally justified and how must hostilities be conducted to be moral. It is the moral analog of the jus ad bellum – the international law governing when States may resort to force – and of the law of armed conflict, also called the jus in bello and international humanitarian law – governing the conduct of the parties during armed hostilities.
In this essay, I step away from the political quarrel to explain the just war doctrine and its sources. I begin by briefly summarizing the doctrine’s origins. I then turn to the Catholic Church’s current position on the doctrine, which lies at the heart of Vance’s comments and underpins Pope Leo’s. Although other Christian and secular variants exist (which are similar), I focus here on the Catholic articulation, especially as reflected in the Church’s Catechism, because the present controversy arises from criticism of the Pope and his appeals to the principles it expresses.
As will become apparent, there is significant overlap between just war doctrine and contemporary international law, especially regarding self-defense under the jus ad bellum and the restraints on the conduct of hostilities in the law of armed conflict. That overlap should not obscure the distinction between the two. Just war doctrine is a moral tradition, not a source of positive international law, although it has helped shape the values that animate both the jus ad bellum and the law of armed conflict. Finally, I will offer my assessment of the Trump administration’s compliance with the just war doctrine, concluding with a few reflections on the debate.
Origins of the Just War Theory
Just war theory emerged in late antiquity as Christian theologians sought to reconcile the New Testament’s stringent strictures against violence with the political reality of governing a Christian empire (classic treatments include Ramsey, Walzer, O’Brien, and Johnson). Saint Augustine of Hippo (354-430) is regarded as the intellectual father of the theory. In works such as The City of God, he argued that although peace must always be the ultimate objective, there are circumstances in which it can be morally required to wage war in order to defend the innocent or restore peace. At the same time, he also understood war as a means of punishing wrongdoing and chastising sinners so as to move them toward repentance and reform.
Following Augustine, just war theory took on a more systematic form. In this regard, Thomas Aquinas (1225-1274), in the Summa Theologiae, identified three conditions for a just war:
(1) sovereign authority;
(2) just cause; and
(3) right intention.
The formulation proved highly influential because it distilled the just war tradition into a structure that enabled assessments of who may wage war, for what reason, and toward what end. Theory was becoming doctrine.
Later writers, such as Francisco de Vitoria (1483-1546) and Francisco Suárez (1548-1617), built on this framework in the context of imperial expansion and the developing law of nations (e.g., Vitoria, De Indis and De Jure Belli; Suárez, De Bello). In doing so, they helped move just war reasoning beyond intra-Christian discourse toward general principles. Hugo Grotius (1583-1645) translated this moral approach into terms that proved foundational for the emerging law of nations (De Jure Belli ac Pacis).
Importantly, these writers understood that just war doctrine needed to address not only the circumstances in which force may be used but also the manner in which war must be fought; war, if it is to be just, must be fought justly. Grotius, in particular, devoted considerable attention to limits on the conduct of hostilities, including principles that presaged what we now call “distinction” (e.g., distinguishing between civilians and legitimate military targets).
These precepts are increasingly reflected in modern international law. They were evident, for instance, in the 1863 Lieber Code and in the Regulations on the Laws and Customs of War on Land, annexed to the 1899 Hague Convention II and the 1907 Hague Convention IV. The law governing the conduct of hostilities continued to develop, particularly through the 1949 Geneva Conventions and the 1977 Additional Protocols, instruments that codify many of the moral constraints and obligations associated with just war doctrine, as well as the traditions of the world’s major religions.
In the 20th century, just war doctrine’s moral constraints on the resort to force underpinned progressive legal codifications. The 1919 Covenant of the League of Nations and the 1928 Kellogg-Briand Pact represented important efforts to restrict war as an instrument of national policy. However, it was the 1945 UN Charter that established a general prohibition on the threat or use of military force, while preserving the “inherent right” of self-defense against armed attack. As noted in the Department of Defense (DoD) Law of War Manual, “Certain jus ad bellum criteria have, at their philosophical roots, drawn from principles that have been developed as part of the Just War Tradition” (§ 1.11.1).
Despite codification and the progressive development of customary law with respect to both the jus ad bellum and law of armed conflict, the just war doctrine remains important as a moral touchstone through which debates over these matters continue to be framed.
Contemporary Just War Doctrine
Contemporary Catholic just war doctrine begins from a presumption against war. That presumption is not pacifism, for the doctrine allows the use of defensive force in exceptional situations. But it means that the burden of moral justification rests on those who would resort to force.
The doctrine itself is set forth in the Church’s Catechism. Thus, when responding to political criticism of Pope Leo’s statements, Bishop James Massa, the chair of the US Conference of Catholic Bishops Committee on Doctrine, cited the Catechism:
For over a thousand years, the Catholic Church has taught just war theory and it is that long tradition the Holy Father carefully references in his comments on war. A constant tenet of that thousand-year tradition is a nation can only legitimately take up the sword ‘in self-defense, once all peace efforts have failed’ (Catechism of the Catholic Church, no. 2308). That is, to be a just war it must be a defense against another who actively wages war, which is what the Holy Father actually said: ‘He does not listen to the prayers of those who wage war.’
Bishop Massa also took the opportunity to remind Vance, “When Pope Leo XIV speaks as supreme pastor of the universal Church, he is not merely offering opinions on theology, he is preaching the Gospel and exercising his ministry as the Vicar of Christ.”
The Catechism is a systematic compendium of the Church’s doctrine, produced by a Commission of Cardinals and Bishops, chaired by then-Cardinal Ratzinger (later Pope Benedict XVI). In 1992, Pope John Paul II promulgated the Catechism; a revised edition was approved five years later. It contains the “essential and fundamental content of the Catholic faith “and presents what Catholics throughout the world believe in common.” The section on “Safeguarding Peace” sets out the Church’s doctrine based on just war theory (pt. 3, sect. 2, ch. 2, art. 5). It appears in the treatment of the 5th Commandment (in Catholic numbering), “You shall not kill.”
In a moral analog to the international law prohibition on the use of force in Article 2(4) of the UN Charter and customary international law, the Catechism’s sub-section on “Avoiding War” begins by noting, “The fifth commandment forbids the intentional destruction of human life,” observing that “evils and injustice accompany all war,” and emphasizing that “all governments are obliged to work for the avoidance of war”(¶¶ 2307-08).
Despite the centrality of avoiding war in Catholic doctrine, the Catechism acknowledges that “as long as the danger of war persists and there is no international authority with the necessary competence and power, governments cannot be denied the right of lawful self-defense, once all peace efforts have failed” (¶ 2308). This moral right is often described in terms of the related but distinct requirements of “just cause” and “right intention.” Just cause asks whether force is being used for a morally permissible reason, paradigmatically, a defense against aggression. Right intention queries whether the force is being used for that reason, rather than as punishment, vengeance, conquest, and the like (although early just war theory countenanced some forms of punitive war, contemporary doctrine rejects that justification). It must be cautioned that some just war theorists also recognize the defense of others, the protection of basic human rights, and humanitarian intervention as possible moral justifications (see my discussion here). However, in the current context, and given that the President quickly abandoned any suggestion that the attack was intended to protect the Iranian people from the government’s deadly crackdown, I deal only with the doctrine’s self-defense justification.
The international law derivative is the right of self-defense, found in Article 51 of the UN Charter and in customary law: “Nothing in the present Charter shall impair the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations, until the Security Council has taken measures necessary to maintain international peace and security.” Note that the reference to an “international authority” in the Catechism aligns with Article 51’s restriction that States may use force in self-defense only until the Security Council addresses the situation.
Like jus ad bellum self-defense, just war doctrine imposes “rigorous conditions of moral legitimacy” on self-defense, given “the gravity of such a decision.” Expressly citing the just war doctrine, the Catechism sets forth four conditions, three of which are unambiguously reflected in contemporary international law (¶ 2309).
1. “The damage inflicted by the aggressor on the nation or community of nations must be lasting, grave, and certain.”
This condition aligns with the legal limitation of self-defense to situations involving a use of force rising to the level of an “armed attack.” In particular, the emphasis on severity is reflected in the International Court of Justice’s treatment of an armed attack as “the most grave form” of the use of force (Paramilitary Activities, ¶ 191). Although the United States does not accept a distinction between the use of force, which is a violation of international law, and an armed attack, which triggers the right to self-defense, its interpretation is in a clear minority among States and international law scholars (DoD Law of War Manual, § 1.11.5.2).
2. “All other means of putting an end to it must have been shown to be impractical or ineffective.”
In the law of self-defense, the equivalent condition is “necessity,” which requires that non-forcible means of addressing an armed attack be exhausted or incapable of dealing with the situation before the right of self-defense allows for a forcible response (on necessity, see Paramilitary Activities, ¶¶ 194, 237; Nuclear Weapons, ¶ 41; Oil Platforms, ¶¶ 43, 73-74, 76).
3. “There must be serious prospects of success.”
The self-defense international law condition of necessity likewise reflects the just war doctrine’s requirement that there be a real likelihood of success. After all, if a defensive use of force is likely to fail, then it is not necessary by definition, for it will not contribute meaningfully to the effective defense of the State.
4. “The use of arms must not produce evils and disorders graver than the evil to be eliminated.”
This condition is not reflected in the law of self-defense. The requirement of proportionality in defensive actions is not about relative harm caused. Instead, jus ad bellum proportionality requires that the force a State uses to defend itself be no more than required in the circumstances to effectively stop an ongoing or imminent armed attack. This may be more than the force being used against the victim State, but it may also be less. The question is how much force is required (as distinct from the necessity condition, which asks whether force is required in the first place). (For an opposing view on the law of self-defense, see Adil Haque’s writings here and here.)
In this regard, though, I note that the DoD Law of War Manual appears to take the view that just war doctrine and jus ad bellum proportionality are aligned (§ 1.11.1.2).
The Catechism provides that the “evaluation of these conditions for moral legitimacy belongs to the prudential judgment of those who have responsibility for the common good.” Similarly, when discussing just war theory, the DoD Law of War Manual characterizes the requirement as “a competent authority to order the war for a public purpose.” The public purpose element is crucial, for it distinguishes the authority to act in defense of the State from violence undertaken for private or personal reasons. It is reflected in the corresponding jus ad bellum principle that “the resort to military force is the prerogative of the State” (§ 1.11.1.1). The DoD Law of War Manual notes that, in addition to being reflected in law, just war doctrine conditions have been incorporated into military doctrine (§ 1.11.1).
Beyond these moral criteria for resorting to force, the Catechism sets out a number of moral obligations that underpin key aspects of the law of armed conflict. It begins by emphasizing that “[t]he mere fact that war has regrettably broken out does not mean that everything becomes licit between the warring parties” (¶ 2312). This is a well-accepted, indeed foundational, premise in contemporary international law. For instance, the DoD Law of War Manual confirms that “States fighting against one another must adhere to rules relating to the conduct of hostilities (jus in bello), regardless of whether a State may be considered the aggressor or whether the initial resort to force was lawful under jus ad bellum” (§ 3.5.2.1).
As to specific rules, the Catechism provides that “Non-combatants, wounded soldiers, and prisoners must be respected and treated humanely;” emphasizes that “[e]very act of war directed to the indiscriminate destruction of whole cities or vast areas with their inhabitants is a crime against God and man, which merits firm and unequivocal condemnation;” and condemns genocide as a “mortal sin” (and holds that “[o]ne is morally bound to resist orders that command genocide”). It also emphasizes that there is no defense of superior orders and that “[a]ctions deliberately contrary to the law of nations and to its universal principles are crimes” (¶¶ 2313 and 2314). Thus, the doctrine not only finds form in the law, but the Catholic Church also holds that it is a moral duty to follow the international law governing the resort to war and warfare itself.
The War in Iran and the Just War Doctrine
In my estimation, there is little doubt that the United States’s use of force against Iran (and Venezuela) violates both international law governing the resort to force and the moral precepts of just war doctrine. That the war is unlawful under jus ad bellum principles is well documented in prior Just Security contributions (see the collection), not least in the letter from over 100 international lawyers, including me. And then there are Trump’s numerous threats. Had some of them been carried out, the resulting operations would have violated the law of armed conflict by the United States and, depending on the facts of each case, would have constituted war crimes and crimes against humanity by those involved, including senior U.S. leadership. Among the most egregious were his threats that, if Iran did not open the Strait of Hormuz, the United States would bomb the country “back to the Stone Age,” and that, if a deal was not reached, “A whole civilization will die tonight, never to be brought back again.” Such attacks would be the very antithesis of the principle of distinction.
Given the congruency noted above between just war doctrine and international law, the same conclusion must be drawn about compliance with the moral dictates of that doctrine. The starting point is the Catechism’s insistence that “all governments are obliged to work for the avoidance of war.” It is difficult to characterize the Trump administration’s approach as one marked by a commitment to avoiding war. The conflict started as negotiations were underway, and the U.S. administration’s rhetoric has consistently been escalatory, as in Hegseth’s claim that “We’re fighting religious fanatics who seek a nuclear capability in order for some religious Armageddon.” Trump’s threats to use massive force to inflict catastrophic suffering on an entire civilization fly in the face of the moral posture of a State that is reluctantly defending itself. And the rhetoric is of a nature that the just war doctrine has long treated with suspicion – domination, humiliation, and the infliction of suffering for coercive effect.
Additionally, just war doctrine does not encompass resorting to force based on speculative future threats, general hostility, support for proxies, or malign regional activities, as in the case of Iran. These factors raise serious security concerns to be sure, but, by themselves or collectively, they do not satisfy the moral requirement that the harm be so grave and certain that acting forcibly in self-defense is necessary. There must be a legitimate need to act defensively (just cause), and that need must be the underlying motivation for the action (right intention).
In this regard, the Administration has failed to offer a coherent case for its actions, with justifications (and claims of success) shifting chaotically. There was no imminent threat to the United States from Iran, nor could cabinet-level officials even rhetorically support one in answering congressional questions. The sole colorable justification for the U.S. attack would have been to defend Israel against an imminent or ongoing Iranian armed attack. But such a future attack was hardly “certain” given the President’s claim following the earlier June 2025 U.S. and Israeli operations that “Iran’s key nuclear enrichment facilities have been completely and totally obliterated,” and many months then passed without any military incident, whether by proxies or otherwise. The White House even released a catalog of supporting statements from other U.S. and Israeli leaders on the successful completion of the June operation. Included was an assertion by the IDF’s Chief of Staff that “I can say here that the assessment is that we significantly damaged the nuclear program, and I can also say that we set it back by years, I repeat, years.” In such circumstances, the U.S. operations fail to satisfy either the just cause or the right intention requirements.
And even if they had been satisfied, the use of force must be a last resort to be just. As noted, negotiations were still underway. And considering the claimed obliteration of the Iranian program during the June 2025 strikes, as well as the fact that hostilities in the region had ebbed (see Yuval Shany and Amichai Cohen’s description of the timeline), it is difficult to see why there was no time to pursue other avenues to address this situation, such as continued diplomacy, sanctions, Security Council engagement, and other non-forcible mechanisms, even if less than perfect. Just war doctrine does not require that a State be naive, nor does it require States to pursue futile negotiations indefinitely. But it does require a clear demonstration that war is a last resort; there is no basis for treating the use of force as a preferred instrument for pressuring another State to act.
The U.S. operations also appear to falter under the just war doctrine’s condition that there be a sufficient prospect of success. While the U.S. armed forces have inflicted extraordinary destruction on the Iranian armed forces and infrastructure, it is difficult to see what they have achieved at the strategic level of war beyond diminishing Iranian military capabilities. And in any event, the success in question must be in achieving a legitimate objective under the just war doctrine, which is not the case here. Under the just war doctrine, the prospect of tactical success does not satisfy this condition.
As noted, the just war doctrine’s characterization of proportionality differs from that in the jus ad bellum in that it requires balancing harm, taking into account human, social, and moral consequences of war. Assuming for the sake of argument alone that the United States did have a just cause and the right intention, and force was a last resort, it would have had to factor in foreseeable harmful consequences from its operations – like harm to civilians and civilian objects, destabilization of the region, the foreseeable threat to global energy supplies, global economic disruption, the risk of broader reciprocal attacks, the intensification of sectarian conflict, and the risk of an escalatory spiral that would be difficult to control. And given the Trump administration’s apocalyptic rhetoric, it must have contemplated the possibility of extreme harm, at least if it is to be taken at its word. To state the obvious, it is simply unimaginable that the destruction of a civilization would be proportionate under the just war doctrine. Nor would be the destruction of that civilization’s ability to generate electricity for its people by wiping out all their power plants.
Finally, if the decision to resort to force is morally defensible under the just war doctrine, which it was not, the conduct of hostilities would remain subject to the doctrine’s moral constraints on how war must be fought. The Catechism’s insistence that those rules continue to govern both sides is of particular importance given the U.S. condemnation of Iran, much of which is fair and accurate. In this regard, the threats made by Trump and other administration officials imply that civilians and civilian objects would be indiscriminately attacked in violation of the just war doctrine. And under that doctrine, members of the armed forces who complied with such manifestly unlawful orders could not escape moral condemnation on the basis that they were merely following orders.
* * *
In sum, assessed against the requirements of the just war doctrine, the Trump administration’s actions clearly fall short. They do not reflect a genuine commitment to avoiding war and have not been justified as necessary in self-defense against lasting, grave, and certain harm. The United States had not exhausted non-forcible alternatives, and its actions were unlikely to produce a just peace. Had Trump’s threats been carried out, there is little question that the consequences would have been graver than those they were purportedly designed to eliminate, and immoral on the basis of being indiscriminate. It seems clear to me that the rhetoric suggests indifference, if not hostility, to the moral limits inherent in the just war doctrine.
Concluding Reflections
While States must be guided by extant international law when considering whether and how to use force, its rules set only the legal boundaries that they may not cross, whether through action or omission. The decisions our leaders make must equally be informed by moral considerations, which seem in short supply in the ongoing conflicts. Just war doctrine helps calibrate the moral compass that should inform such decisions and serves as a useful framework for balancing military and humanitarian considerations when interpreting international law rules that may not offer clear guidance in the attendant circumstances. Despite the Vice President’s pontification on the matter, I will stick with the views of the Pontiff on the interpretation of the doctrine.
As to the broader dispute between the Trump administration and the Holy See, it is worth remembering that Popes have been instrumental in advancing positive political change. The obvious example is Pope John Paul II, who, by championing human rights, self-determination, and religious freedom, played a pivotal role in undermining autocratic communist regimes and fostering democracy in the former Soviet Union, Eastern Europe, and beyond. Pope Leo is following in this proud tradition in speaking out on issues of war and peace.
Lastly, with regard to the ongoing conflict between the United States and Iran, David Brooks insightfully observed on the PBS NewsHour Friday that we are seeing a “contrast between the way Trump has gone into this war, which is cavalier in the extreme, and Catholic just war theory, which traces back to Augustine and Aquinas, [and] which is intellectually rigorous.” This leads him to conclude, rightly so in my opinion, that the Pope is “trying to put [in place] an intellectual, rigorous process on how you evaluate a very deadly policy. And the Trump administration is completely incapable of thinking in these terms.”
It seems appropriate to close this essay on the Trump administration and the Catholic Church with an extract from the Catechism itself (¶ 2317):
Injustice, excessive economic or social inequalities, envy, distrust, and pride raging among men and nations constantly threaten peace and cause wars. Everything done to overcome these disorders contributes to building up peace and avoiding war.
You don’t need to be Catholic to grasp the wisdom of the observation.
– Michael Schmitt, Published Courtesy of Just Security.
