Thank you for inviting me to join you and share my thoughts on a question older than the modern state, older than the Westphalian settlement, older even than the constitutional architecture whose defense occupies so much of our professional life. It is the question whether war—terrible, convulsive, morally dangerous war—can ever be just. The question is not the property of theologians alone, nor of philosophers, nor of generals, nor of lawyers. It belongs to civilization itself. For as long as men have taken up arms, they have also felt the need to explain why they did so and to distinguish the soldier from the brigand, the magistrate from the murderer, the defense of justice from the intoxication of conquest.
Homer’s Iliad, among our earliest literary meditations on war, does not present combat as a mere arithmetic of power. Achilles is not simply strong; he is wrathful. Hector is not simply brave; he is bound by duty, city, family, and honor. Even in that heroic and savage world, there were standards—sometimes observed, sometimes violated—about reasons for fighting and conduct in battle. The ancient mind, no less than the modern conscience, knew that war is never morally self-authenticating. The mere fact that a nation can fight does not mean that it may fight. And the mere fact that it may fight does not mean that it may fight in any fashion it pleases.
Just War Theory: A Framework of Moral Judgment
That intuition, disciplined by Christian theology, refined by natural law, translated into international law, and embodied in our own constitutional structure, is what we call Just War Theory. It is not a hymn to militarism. It is not a warrant for adventurism. It is not the moral equivalent of a blank check drawn on Providence and payable to the ambitions of statesmen. Properly understood, it is a restraint on power, a framework of moral judgment, and a stern reminder that the sword, even when lawfully borne, remains an instrument to be feared.
We live in an age in which the old temptations return wearing new garments. The lust for dominion appears now not only in armies and ideologies, but in algorithms, autonomous systems, drone swarms, cyber operations, and artificial intelligence tools capable of compressing the time between suspicion and destruction. In such an age, just war principles are not antiquarian ornaments. They are indispensable safeguards of human dignity and constitutional government.
Just War Theory is rooted in the Christian tradition, especially through Roman Catholic theology. The Catholic tradition begins not with a romantic view of war, but with a sober anthropology. Man is made in the image of God; man is also fallen. Political authority exists to secure the common good, but political authority itself is susceptible to vanity, fear, ideology, and the libido dominandi—the lust for power. Thus, the tradition refuses both pacifist abstraction and bellicose enthusiasm. It recognizes that peace is the normal object of political order, yet it concedes that force may be necessary to defend the innocent, punish grave wrongs, and restore a peace shattered by aggression.
The Old Testament presents episodes of fearsome violence, including the Battle of Jericho in Joshua 6. But those episodes cannot serve as a license for modern states to wage annihilating wars. Israel, in those accounts, is a theocracy acting under divine command. No temporal sovereign may claim the authority of God over life and death. The lesson is not that rulers may slaughter at will. It is precisely the opposite: Temporal power is limited power, and the resort to arms requires moral justification.
Saint Augustine was the first great Christian thinker to give systematic attention to the possibility of a just war. He did so reluctantly as one who understood that even a justified war is a calamity. For Saint Augustine, war may be tolerated only to avert greater injustice and to preserve or restore a minimal order without which human flourishing becomes impossible. He wrote in Contra Faustum that “[t]he natural order conducive to peace among mortals demands that the power to declare and counsel war should be in the hands of those who hold the supreme authority.”[REF] That sentence contains a proposition of enduring constitutional significance: War must not be privatized. It must not be left to factions, companies, private militias, or mobs. The sword belongs to lawful authority, and lawful authority bears responsibility before God, law, and the political community.
Augustine also insisted on just cause. In his commentary on Joshua, he described a just war as “one that avenges wrongs, when a nation or state has to be punished, for refusing to make amends for the wrongs inflicted by its subjects, or to restore what it has seized unjustly.”[REF] A war of conquest, aggrandizement, or plunder cannot satisfy that test.
Finally, Augustine demanded right intention. In his letter to Boniface, he admonished: “Peace should be the object of your desire; war should be waged only as a necessity and waged only that God may by it deliver men from the necessity and preserve them in peace. For peace is not sought in order to the kindling of war, but war is waged in order that peace may be obtained.”[REF]
Legitimate Authority, Just Cause, and Right Intention
Here is the Augustinian genius: Motive matters. A state may possess an army, a casus belli, and a plausible strategic objective and still act unjustly if animated by vengeance, cruelty, or domination. War must not become the sacrament of national self-worship. Necessity, not will, must slay the enemy. Mercy must discipline victory.
Saint Thomas Aquinas, in the Secunda Secundae of the Summa Theologica, Question 40, “De bello,” took Augustine’s scattered insights and gave them scholastic precision. Aquinas identified three necessary conditions: legitimate authority, just cause, and right intention.
On legitimate authority, he taught that only the sovereign charged with care of the common good may declare war.[REF]
On just cause, he wrote that “a just cause is required, namely that those who are attacked, should be attacked because they deserve it on account of some fault.”[REF]
On right intention, he wrote that “it is necessary that the belligerents should have a rightful intention, so that they intend the advancement of good, or the avoidance of evil.”[REF]
Aquinas’s discussion of self-defense also brings us to the Principle of Double Effect. An act may have both good and evil effects. It may be permissible only if the act itself is good or morally neutral; if the actor intends the good effect and merely foresees, without intending, the evil effect; if the evil effect is not the means to the good end; and if there is proportionate reason for permitting the evil effect. The tactical bomber who strikes a military target while foreseeing but not intending civilian casualties is not morally identical to the terrorist bomber who seeks civilian death as an instrument of coercion. The outward act may resemble itself; the moral object does not.
Later thinkers, including Francisco de Vitoria and Hugo Grotius, clarified additional criteria: proportionality, reasonable chance of success, and last resort. These were not alien grafts upon the tradition. They were refinements of its central premise: War is not an ordinary tool of policy, but an extraordinary and tragic instrument whose moral legitimacy depends upon strict conditions.
The Catechism of the Catholic Church gives the classical doctrine its contemporary formulation. Paragraph 2309 outlines the four strict traditional conditions required for legitimate defense by military force. It states that “[t]he strict conditions for legitimate defense by military force require rigorous consideration.” It requires (1) that “the damage inflicted by the aggressor…must be lasting, grave, and certain;” (2) that all other means of ending it have proved “impractical or ineffective”—the “last resort” doctrine; (3) that there “be serious prospects of success;” and (4) that “the use of arms must not produce evils and disorders graver than the evil to be eliminated.” It adds that “the power of modern means of destruction weighs very heavily in evaluating this condition.”[REF]
That last sentence deserves our attention. The tradition is not frozen in amber. It does not ask us to pretend that a sword, a musket, a bomber, a nuclear missile, a cyber weapon, and an autonomous drone present identical moral problems. The principles endure, but their application mu
