Did Pope Leo Reject Just War Theory?

The short answer is no.

Here is a good article by an Irish theologian/professor in Ireland, published in the Jesuit magazine America. The link should work even if you are not a subscriber. There is more to the article then what I have excerpted.

Ever since the United States and Israel initiated “Operation Epic Fury” against Iran on Feb. 28, we had already witnessed a resurgence of discussion of just war theory. I have read over 100 articles, opinion pieces and interviews during this time in which just war criteria were used either to criticize or to justify the war—from theologians, philosophers, ethicists, politicians and pundits to priests, bishops, archbishops and Vatican officials.

Some politicians—like President Donald J. Trump, White House adviser Stephen Miller and Secretary of Defense Pete Hegseth—have made no pretense about respecting or adhering to just war principles, the international laws of war and rules of engagement. However, both Vice President JD Vance and Speaker of the House Mike Johnson have mentioned just war theory—although without attending to its principles—in response to remarks by Pope Leo XIV that God is “never on the side of those who yesterday wielded the sword and today launch bombs.” 

“Magnifica Humanitas” asked a different question, however. Is just war theory still relevant? One sentence in paragraph 192 of the encyclical drew inordinate attention: “Today, more than ever, without prejudice to the right to self-defense in the strictest sense, it is important to reaffirm that the ‘just war’ theory, which has all too often been used to justify any kind of war, is now outdated.” Just this past weekend, Pope Leo also told journalists that “the just war theory comes from centuries past when we couldn’t imagine the weapons [and] human beings’ ability for destruction.”

When Pope Leo notes in “Magnifica Humanitas” “the right to self-defense in the strictest sense,” we see the obvious evidence that he still recognizes what the Catechism refers to as “the strict conditions for legitimate defense,” which are “are the traditional elements enumerated in what is called the ‘just war’ doctrine” (No. 2309). These criteria include just cause, last resort, proportionality, the probability of success, legitimate authority and noncombatant immunity, with right intent implied under the heading of “safeguarding peace.” 

A major concern in this section of the encyclical is the “normalization of war” (Nos. 189-192). Pope Leo writes, “When historical memory fades and the ethical principles that protect civilians and the most vulnerable are weakened, it becomes easier to justify violence as necessary, inevitable or even ‘sanitized’” (No. 192). Two paragraphs earlier, he similarly observes, “Today, however, we are witnessing a real paradigm shift in public discourse and in decisions regarding rearmament, with a troubling revival of war as an instrument of international politics, while the very ethical principles that had previously limited its use are being eroded” (No. 190). 

Yet it is important to remember a point the Jesuit theologian John Courtney Murray noted about the violations of just war principles during the Second World War: “This is no argument against the traditional doctrine. The Ten Commandments do not lose their imperative relevance by reason of the fact that they are violated.” Rather than saying the ethical criteria of just war theory are outdated, the answer is to emphasize their proper use, and to teach the just war doctrine more rigorously as well as to clearly expect more stringent adherence to it.

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Interestingly, there is no explicit reference to pacifism or nonviolence in the encyclical. In an implicit use of the criterion of probability of success, Pope Leo writes, “Humanity possesses far more effective and capable tools for promoting human life and resolving conflicts, such as dialogue, diplomacy and forgiveness” (No. 192). The emphasis on peacebuilding, diplomacy, conflict prevention and international law (No. 203) also helps render armed force truly a last resort. Still, ever since his first “Urbi et Orbi” blessing at Easter a year ago, Leo has frequently used “the expression ‘to disarm,’ which is close to my heart” (No. 110). While this may sound like nonviolence or pacifism, I don’t think this is what the expression means.

After all, St. John Paul II, in his 2000 World Day of Peace message, wrote in regard to humanitarian intervention in cases of genocide and crimes against humanity: “Clearly, when a civilian population risks being overcome by the attacks of an unjust aggressor and political efforts and non-violent defense prove to be of no avail, it is legitimate and even obligatory to take concrete measures to disarm the aggressor,” a point that was echoed in the Compendium of the Social Doctrine of the Church (No. 506). In 2014, on the question of what should be done about the genocidal violence of ISIS against ethnic and religious minorities in northern Iraq, Archbishop Silvano Tomasi said that “when all other means have been exhausted, to save human beings the international community must act. This can include disarming the aggressor.”

For his part, instead of “disarming,” Pope Francis said, “In these cases where there is unjust aggression, I can only say that it is licit to stop the unjust aggressor. I underscore the verb ‘stop’; I don’t say bomb, make war—stop him.” He added, “The means by which he may be stopped should be evaluated,” and he expressed his concern that “powerful nations” abuse this rationale of “stopping an unjust aggressor” for ulterior motives, such as conquest.