Even as modern warfare becomes more technologically advanced, with the U.S. military employing drones and artificial intelligence in Iran, an ethical framework that dates to the fifth century is still being invoked when war breaks out.
The “just war theory” originated with Augustine of Hippo, a Catholic bishop and who laid out arguments for “righteous war” that were later expanded upon by Thomas Aquinas and other medieval theologians.
The basic tenets are these: for a war to be considered just, it must be in response to a significant threat, the military action must be proportional to the threat, there must be a reasonable chance of success and innocent people must not be harmed.
At the time these principles were first conceived, wars were fought by men who killed each other with spears, swords and arrows. Today, they are discussed as pundits watch explosions in distant lands on their cellphones.
And they are used not only as justifications for war, but also to excuse it, some say.
“Most politicians are fine with such ‘just war’ discourse because it allows those with direct decision-making responsibility to interpret and even spin these criteria to maintain their war-making, either now or in the future,” Eli McCarthy wrote last month for The National Catholic Register.
Just-war theory matters because it brings sobriety and time-tested precepts into a discussion that is at times both bellicose and religious in nature, said Michael Kryzanek is professor emeritus of political science at Bridgewater State University in Massachusetts, noting Secretary of Defense Pete Hegseth’s recent prayer for “overwhelming violence of action against those who deserve no mercy.”
“All of a sudden these religious words … have entered into the discussion of whether this war indeed is moral or immoral, just or unjust, and that has not been the case in other warfare in modern times," Kryzanek said. “That’s a new step along the way, and I think this might be the unfortunate wave of the future. Not that I’m opposed to religion; I’m opposed to using it for the purpose of justifying the dark side of warfare: killing, bombing and the like.”
In a recent essay, Kryazanek, who was formerly the executive director of the Minnock Center for International Engagement at Bridgewater State, argued that the U.S. and Israeli action in Iran does not meet the criteria for a just war.
Catholic Bishop Joseph Strickland said much the same on a recent podcast, telling Tucker Carlson, a staunch critic of the war, “There probably aren’t many wars in human history that would qualify as meeting all the criteria” and saying that world leaders should “look more deeply” into the principles of just war.
Others, however, are arguing that the criteria have been met with regard to Iran, even with regard to proportionality.
So, as one scholar of just-war theory once asked, “What would Augustine do?”
The origins of ‘Just War Theory’
In the beginning of his 1977 book “Just and Unjust Wars,” Princeton scholar Michael Walzer quotes a Latin maxim attributed to Cicero: Inter arma enim silent leges, which means “In time of war, the law is silent.”
The idea is, Walzer writes, that “War is a world apart, where life itself is at stake, where human nature is reduced to its elemental forms, where self-interest and necessity prevail.”
Despite that, “For as long as men and women have talked about war, they have talked about it in terms of right and wrong,” even in the ancient world.
But it wasn’t until the 5th century that a “coherent Christian framework” based on three pillars arose in the work of Augustine, according to Harvard professor Mathias Risse, who writes:
“First, war can sometimes be morally permissible when it is ordered in pursuit of peace or justice. Second, even a just war cannot be initiated or conducted by just anyone: it requires right authority, that is, authority exercised by properly accredited leaders. Third, Augustine insisted that just cause and rightful authority alone are insufficient: there must also be right intention. War must not be waged in a spirit of hatred or cruelty; its aim must be the restoration of order, not vengeance.”
Those principles became a foundation on which others built on, including Thomas Aquinas in the 13th century and Dutch lawyer and philosopher Hugo Grotius in the 17th century, which is why discussions of just-war theory may cite three core principles, or four or six. The need to protect innocents is often included in such discussions, as well as the need for proportionality, which means the harms of war must not be greater than the good it seeks to accomplish.
Just-law theory remains, however, a “tradition of thought,” not a legal doctrine, “although the law of war accepts some of its precepts,” David Luban, Distinguished University Professor at Georgetown Law School, said in an email.
Modern interpretations break it into two categories: jus ad bellum (justice of war) and jus in bello (justice in war); the former involving the ethics of launching military attacks or declaring war, the latter involving ethical combat.
It is the justice of war, or JAB, that is at the forefront of conversation, as the military action in Iran continues, and Luban says six principles are involved here — Augustine’s just cause, legitimate authority and right intention; the rule of proportionality; and two others: the use of force is the last resort, and there is a reasonable hope of success.
“Since World War II and the UN Charter, it’s generally agreed that the only just cause is self-defense — not revenge, not punishment, not grievances unrelated to defending against armed attacks," Luban added.
He noted that the basic principles of just cause are contained in the UN Charter, “which forbids threats of force and use of force against the territorial integrity and political independence of another state” unless a state is acting in self-defense against an attack.
“Launching an attack that isn’t in self-defense is prohibited as aggression — and in the Nuremberg Charter, aggression (known there as ‘crimes against peace’) is a serious violation," Luban said.
Is Operation Epic Fury ‘just’?
The Trump administration has argued that its action in Iran is, in essence, self-defense. In a video posted on social media on Feb. 28, the day the military operation began, President Donald Trump said, “Iran’s menacing activities directly endanger the United States, our troops, our bases overseas, and our allies throughout the world.”
And in his speech to the nation Wednesday evening, Trump spoke of “Iran’s sinister threat to America and the world” and said the objective of Operation Epic Fury is “systematically dismantling the regime’s ability to threaten America or project power outside of their borders.”
Writing for Providence magazine, Gregory J. Moore, chairman of the Department of Government at Patrick Henry College in Virginia, argued that the United States is operating within the parameters of just-war theory with regard to self-defense.
“First, Iran declared war on the United States in 1979 when the Shiite clerics under Ayatollah Khomeini took power, chanting “Death to America,” storming the U.S. Embassy in Tehran, and taking 66 Americans hostage. Iran was also responsible for the deaths of 220 U.S. Marines and 21 other U.S. military members in its attack on U.S.forces in Beirut in 1983," Moore wrote in Providence, a journal published by The Institute on Religion and Democracy.
He went on to cite other Iran-backed attacks on Americans, its support of terrorist organizations, and its quest to develop nuclear weapons.
“Indeed, the U.S. has had a rationale for attacking Iran in the sense of self-defense for some time,” Moore said. He also argues that Operation Epic Fury meets the just-war standards of proportionality, right intentions and last resort.
Others strongly disagree.
Writing for the journal Public Discourse, Christopher Tollefsen grappled with whether the killing of Iran’s Supreme Leader Ali Khamenei was morally justifiable. He concludes not, writing, “It should be clear from the argument thus far that a necessary condition for the just killing of the leader of a nation with whom we are at war is that we are indeed fighting a just war.”
And there are many reasons to doubt that this is the case, wrote Tollefsen, a philosophy professor at the University of South Carolina and director of the school’s Center for American Civic Leadership and Public Discourse.
“This war does not appear to be genuinely defensive against an imminent threat; it is rather undertaken to prevent a threat that might, at some time in the future, materialize, and is therefore a ‘war of choice.’ Natural law just war theory acknowledges no such category: justified warfare is always a matter of necessity.”
Just-war theory and modern warfare
The application of just-war principles to modern warfare are expanding the theory’s reach; while the theologians who built its foundation might not understand today’s weaponry, they’d still recognize the moral arguments surrounding their use.
But as Luban wrote for Boston Review during the presidency of Barack Obama, as the U.S. was targeting and killing al Qaeda operatives with drones, “On these issues Augustine and Aquinas offer scant guidance.”
Bridgewater State’s Kryzanek, however, noted that the current leader of the Catholic Church, Pope Leo XIV, had offered guidance in the form of strong words directed at the Trump administration. The pope has repeatedly called for an end to the conflict and said on Palm Sunday that God “does not listen to the prayers of those who wage war.”
While Kryzanek does not believe the U.S. action in Iran qualifies as just, he says there are questions he says everyone should consider, such as, “Was there another way this could have been achieved in order to order to weaken the regime?” rather than a bombing campaign with civilian fatalities that reportedly include children.
That said, if a lasting peace is eventually the outcome, his assessment — and that of others who consider the military action unjust — might change. But while hoping for it, Kryzanek is not counting on that outcome. “Peace is not a stalemate,” he said.