Over ten years ago, writer and cultural analyst Douglas Murray warned that when Iran became close to acquiring nuclear weapons, Israel would strike and, if necessary, strike alone.

Has that moment arrived? If so, would that justify the decapitation of Iran’s leadership, the “carpet” bombardment of the country, the environmentally destructive attacks on its oil wells, and the major disruption to life across many parts of the globe?

The first question isn’t possible to answer definitively at this point, but it can be said with greater assurance that a nuclear armed Iran—with its self-defining hatred of Israel (“the little Satan”), the U.S. (“the great Satan”), and potentially other “infidel” nations—poses a lethal threat to the world order.

To discuss how this war is justifiable according to just war doctrine, in terms of both theology and international law, it is necessary to start with the working assumption that Iran is indeed on the cusp of developing nuclear power at a level capable of producing the atomic bomb. If it proves otherwise, then of course there is little question that the attack on Iran fulfilled none of the conditions for a just war.

We don’t have to rely on the word of Donald Trump and Benjamin Netanyahu alone to adopt the hypothesis that Iran is perilously close to nuclear weapons. The International Atomic Energy Agency says that Iran’s uranium is enriched to 60%. That level of enrichment means Iran has the capacity to make an atomic bomb. However, it may be that many of the other facilities needed to deploy nuclear weapons have been destroyed in the Israeli attacks of June 2025. Trump at the time claimed Iran’s nuclear threat was “obliterated.” We know Trumpian rhetoric is a bad fit with the facts, so we can’t base our arguments on anything he says, whether it suits us to do so or not.

So, Trump’s spin aside, we the public are left with a reasonable degree of certainty that Iran’s uranium enrichment is at a lethal level but have no way of knowing how much of an imminent threat that constitutes, given that the associated infrastructure and many of the leading scientists have been forensically targeted in “the twelve day war” of almost a year ago. Only the Pentagon and Israel have that information.

Nuclear weapons are considered the ultimate deterrent under normal conditions. Mutually assured destruction is the guarantee they won’t be used by either side. In President Kennedy’s inaugural address in 1961, he declared that “only when our arms are sufficient beyond doubt, can we be certain beyond doubt we’ll never have to use them.”

Iran, however, is an outlier in that respect. Iran’s brand of militant, Shia Islamist extremism has what Dr. Gavin Ashenden describes as “an apocalyptic agenda,” a readiness to self-destruct if it brings about the annihilation of the enemy. We have seen something of this in the mentality of suicide bombers. How much this really scales up is difficult to say. Would Islamist elites be prepared to sacrifice themselves the way they sacrifice their underlings? There are few, if any, commentators, however condemnatory of Israel, who will express any ease at the prospect of Iran acquiring nuclear weapons.

On the assumption that Iran has reached or is close to this tipping point, we can apply the criteria of both the Catholic Church and international law respectively. The Catholic Church’s doctrine is based on St. Augustine’s theory of just war, later refined and expanded by St. Thomas Aquinas. Both of them were clear that a just war could be offensive as well as defensive. “Avenging wrong” and “punishing wrongdoing” are phrases from their writing that make this clear. Such terms could arguably give legitimacy to a war on Iran following the brutal and lethal suppression of civil protests earlier this year, without any necessity to consider whether or not Iran was close to developing nuclear weapons. The conditions of just war and good intention would at least be satisfied.

In the context of a brutal regime with the capacity to make and deploy nuclear weapons—in the teeth of sustained worldwide opposition—it can also be reasonably concluded that dialogue and efforts to negotiate have run into the sand, and so the threshold of last resort is also met.

The condition of proportionality, however, is more difficult to determine, especially in 21st century conflicts. Israel’s operations in Gaza show how complex that can be. Punishing the guilty without inflicting suffering on a great many civilians may not be possible at all when the preservation of their own people is not a priority for the power under attack. Again, assumptions that apply in most situations don’t cover the outliers.

According to St. Augustine, a just war also requires that those waging it have legitimate authority. While both the American and Israeli rulers are elected democratically, the legitimacy of the war requires that the American president secure first the approval of the U.S. House of Representatives. This didn’t happen. Furthermore, in a more globally integrated world than either Augustine or Thomas Aquinas could anticipate, both Israel and the US should also have sought the approval of the UN, something that didn’t happen either.

When dealing with an outlier adversary, it is difficult to comply with any rules. Usually, indications that a country’s government is seeking approval for war creates a final incentive for the intended adversary to seek a way to avoid it. However, there are situations where the loss of the element of surprise may render some war objectives impossible. For instance, targeting the leadership as a way of limiting engagement, which happened in Venezuela and in Iran initially, would be more difficult to achieve if there was forewarning.

A final condition to be satisfied is that a just war must have a strong likelihood of accomplishing its just objectives and restoring peace. The ability to predict the outcome of any war with any degree of assurance is made much more difficult by the fractured and complex political entities in the current theatres of conflict, widely scattered proxies, rapidly evolving war technologies, and outside players pitching in opportunistically.

In the just war doctrine that underpins international law, the bar is even higher, and Pope Leo appears to rely on this in his recent statements—even more than the Church’s teaching. According to this view, after exhausting peaceful means towards resolution, military operations must be limited to defensive, not offensive, action, to resistance to attacks on one’s own lawfully held territory or one’s own people.

Clearly, international law, just as much as theology first shaped in the patristic age, doesn’t answer to many of the scenarios that present in 21st century conflicts. If military action is strictly limited to the defensive, how can countries effectively respond to the threat of nuclear destruction from despots determined to use it once acquired?

Even though this may be the reality of what now confronts Israel, the U.S., and ultimately, perhaps, Europe, Pope Leo has said that the prayers of those “who wage war” are not heard by God. The Pope’s words must be interpreted in the current situation, since that was the context of his remarks. Does he mean that this offensive against Iran is without all justification? It would appear so.

It’s hard to know how much information he has about the level of Iran’s threat. His words may be well substantiated, but he has offered no public substantiation. Perhaps, in general, it’s best for popes and religious leaders to confine their comments to general principles to enable their members to reach as informed a view as possible on current wars, rather than offering what may turn out to have been an inadequately grounded opinion?

Of course, the threat from Trump to obliterate Iranian civilisation summarily, something specifically condemned by the Pope, is well beyond all justification unless one can confidently say that the destruction involved would be less than the destruction of a similar strike on Israel and that such a strike was certain. That sort of macabre calculus shows how complex to intractable the ethical dilemmas are in the era of rapidly advancing technological innovation.

In the present fraught debate one has to ask how much of it is muddied by undue focus on the grotesque rhetoric and demeanour of Donald Trump, the principal player in the psychodrama accompanying this war? Outrageous threats of imminent, mass destruction from Trump do not necessarily equate with an intention to execute them. This has proven to be the case, at least so far, in this conflict. In fact, such a threat in the past by him was an extreme form of sabre rattling designed to unsettle the enemy and make him desist. Trump has spoken about warning Vladimir Putin, during the former’s first presidential term, that he would bomb Moscow off the map if he continued his incursion into Ukraine. Knowing Trump’s volatile and unpredictable character, this may well be what stayed Putin’s course during the years of the first Trump presidency.

All we know is that Putin, for whatever reason, waited for Biden to enter the White House before resuming his attack on Ukraine. Trump, with uncharacteristic self-awareness, said afterwards that Putin couldn’t judge if he meant what he said or not. So, blustering threats from a head of state like Trump may well be an effort to de-escalate rather than a declaration of intent.

Like ethical questions across many other areas of life today, it is extremely challenging to apply principles developed in very a different time to contexts that couldn’t even be envisaged less than a century ago. Developments in military technology, information technology and biotechnology raise new ethical questions and, not infrequently, fall outside the compass of traditional ethical guidelines.

Pope Leo’s early remarks on the war focused on calls for peace and dialogue before he specifically critiqued the war in terms of just war doctrine. Calls for peace and the dialogue needed to secure it are things to encourage always between people of different cultures and traditions. At a time of sharply polarised conflict, they can ring hollow especially in the ears that need to heed them. They can imply a sort of moral equivalence between both sides, like Trump’s frequent calls for peace and dialogue to both Russia and Ukraine, as if one wasn’t clearly the aggressor.

We live in complex times where all the old moral metrics don’t seem to apply neatly anymore. Perhaps, it’s prayer and calls for prayer, reflection, and discernment that’s needed at this moment—more than admonishment from religious leaders.