https://www.nytimes.com/2026/04/23/opinion/trump-iran-unjust-war-catholicism.html
"...But while the manner of a leader matters, the substance matters even more. The debate raises two key questions. First, is Trump’s war on Iran a just war under Catholic just war doctrine? Second, why is Catholic doctrine relevant to anyone other than Catholics? Trump isn’t Catholic, and it’s not clear whether ordinary Americans should care if, say, Catholic officials like JD Vance and Marco Rubio are out of line with Catholic teaching for supporting Trump’s war.
The core requirements of just war doctrine were outlined by Thomas Aquinas in Summa Theologica, in the 13th century. For a war to be just, it must be waged through the lawful operation of the sovereign, it must be waged for a just cause (such as self-defense), and it must be waged for a just purpose.
As the Catechism of the Catholic Church demonstrates, rulers aren’t given broad discretion to decide for themselves what is just...The gravity of such a decision makes it subject to rigorous conditions of moral legitimacy.”
That means that each of the following conditions must be satisfied before a nation engages in armed conflict:
“the damage inflicted by the aggressor on the nation or community of nations must be lasting, grave and certain;
“all other means of putting an end to it must have been shown to be impractical or ineffective;
“there must be serious prospects of success;
“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.”
When you read the Catechism of the Catholic Church you can immediately see why it’s relevant to non-Catholics. Right there in the document are the moral foundations of the modern law of armed conflict.
In fact, the Department of Defense Law of War Manual describes the just war doctrine as part of the “philosophical foundation” of the law of war and says, “The just war tradition remains relevant for decisions to employ U.S. military forces and in warfighting.”
The best piece I’ve read that applies those principles to the Iran war is by Edward Feser, a Catholic philosophy professor at Pasadena City College and the author of “Aquinas: A Beginner’s Guide.” It appeared in Public Discourse, a journal published by the conservative Witherspoon Institute...."
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