(The Conversation) \u2014 Since the beginning of the Iran war, Pope Leo XIV has frequently called for peace, cautioning that the \u201cdelusion of omnipotence<\/a>\u201d makes military force seem preferable to diplomacy. Although U.S. Vice President JD Vance, a Catholic, criticized some of the pope\u2019s comments<\/a>, a growing choir of Catholic voices has criticized the conflict by invoking the concept of \u201cjust war<\/a>\u201d \u2013 an evolving tradition that has guided Christian thinking about war and peace for 1,500 years.<\/p>\n In March, the archbishop of Washington said the war failed \u201cto meet the just war threshold<\/a>.\u201d A month later, the prelate leading the U.S. military\u2019s Catholic chaplaincy delivered a stark assessment: The war was not justified<\/a>. The Vatican\u2019s secretary of state<\/a> raised similar concerns.<\/p>\n Many faiths have teachings about when war is or is not considered justified, including Judaism<\/a>, Islam and Hinduism<\/a>. In the Christian just war tradition, battle is never holy \u2013 \u201cGod does not bless any conflict<\/a>,\u201d in Leo\u2019s words \u2013 but it is sometimes considered necessary.<\/p>\n That tradition traces its roots to the fifth-century theologian St. Augustine<\/a>. A millennium later, St. Thomas Aquinas<\/a> systematized the church\u2019s just war teachings<\/a>, establishing three basic criteria to assess the justifiable use of force: authority, cause and intention. Over time, three more principles emerged: proportionality, last resort and likelihood of success.<\/p>\n Here\u2019s how they could apply today:<\/p>\n Historically, the conversation about a war\u2019s justness began by asking whether a responsible sovereign had declared it.<\/p>\n Today, some just war scholars argue only the United Nations<\/a> holds this authority, since the U.N. charter<\/a> forbids the use of force against another nation except for self-defense.<\/p>\n In the United States, the boundary between presidential and congressional authority for war is contested. According to the U.S. Constitution, only Congress can declare war<\/a>, and Congress controls military funding. Yet the Constitution simultaneously grants the president broad authority to command military operations<\/a>.<\/p>\n President Donald Trump speaks during a news conference at the White House on April 6, 2026, in Washington, as Defense Secretary Pete Hegseth and Chairman of the Joint Chiefs of Staff Gen. Dan Caine listen.<\/span> The 1973 War Powers Resolution<\/a> attempted to balance these principles by requiring presidents to seek congressional authorization for any use of force lasting more than 60 days<\/a>.<\/p>\n Traditionally, Christian theologians argued that self-defense and righting wrongs<\/a> could justify war.<\/p>\n Some causes can never be just. For example, the 16th-century scholar Francisco de Vitoria<\/a> explicitly ruled out \u201cdifference of religion\u201d and \u201cenlargement of the empire<\/a>\u201d as legitimate causes for war.<\/p>\n The Trump administration has offered numerous and shifting<\/a> rationales for the Iran war \u2013 even humanitarian ones, telling Iranians suffering under a brutally oppressive regime<\/a> that \u201cthe hour of your freedom is at hand<\/a>\u201d \u2013 which makes it difficult to assess the justness of its cause.<\/p>\n One of the main explanations U.S. officials have offered, for example, is self-defense. On the war\u2019s first day, Trump declared the objective was to eliminate \u201cimminent threats from the Iranian regime<\/a>.\u201d International law and the just war tradition uphold states\u2019 right to self-defense.<\/p>\n But the law permits force only when necessary to end an ongoing attack or to avert an imminent one<\/a>. And Secretary of State Marco Rubio said the U.S. attacked because of a planned Israeli strike<\/a>, casting doubt on the idea of imminent threat: \u201cWe knew that if we didn\u2019t preemptively go after (Iran) before (Israel) launched those attacks, we would suffer higher casualties.\u201d Pentagon briefers also told Congress the Iranian threat was not imminent<\/a>.<\/p>\n In addition to self-defense, Trump claimed a need to prevent future threats \u2013 otherwise called preventive war<\/a> \u2013 such as nuclear weapons<\/a> or longer-range missiles<\/a> that could reach the United States.<\/p>\n Iran has a history of covert nuclear research<\/a>, which it claims is for civilian use. Experts debate how long it would take<\/a> for the country to produce a nuclear weapon. In 2025, the International Atomic Energy Agency declared Iran was not complying with agreements<\/a> on nuclear nonproliferation. However, international law prohibits preventive war<\/a>.<\/p>\n Trump has also stated that the war would ensure Iran cannot support \u201cterrorist proxies\u201d abroad<\/a>. The regime funds and equips<\/a> Hamas and the Lebanese militant group Hezbollah<\/a>.<\/p>\n Mourners carry the coffins of Hezbollah fighters killed in the war between Hezbollah and Israel during a funeral in Kfar Sir, Lebanon, on April 21, 2026.<\/span> This is a gray area of international law<\/a>, but providing financial and material aid alone is generally not considered sufficient justification for an attack.<\/p>\n Just cause alone is insufficient to render a war just.<\/p>\n Aquinas cautioned that even a war declared by a \u201clegitimate authority, and for a just cause\u201d could \u201cbe rendered unlawful through a wicked intention<\/a>.\u201d Augustine saw love of violence, cruelty or power<\/a> as evil intents. \u201cThe common good of the commonwealth\u201d should motivate the decision to go to war, wrote Vitoria<\/a>, the 16th-century theologian \u2013 not the leader\u2019s personal gain or honor.<\/p>\n Assessing right intent is hard, but a government\u2019s conduct and rhetoric can offer clues. Attacks on civilian infrastructure<\/a>, for example, cast doubt on the Trump administration\u2019s humanitarian claims.<\/p>\n In March, the president told the Financial Times that \u201cmy favorite thing is to take the oil in Iran<\/a>.\u201d In an April post on Truth Social<\/a>, he wrote, \u201cWith a little more time, we can easily OPEN THE HORMUZ STRAIT, TAKE THE OIL, & MAKE A \u2060FORTUNE.\u201d Pursuing economic interests<\/a>, however, would violate right intent.<\/p>\n War is always destructive<\/a>. But today\u2019s Catholic Catechism<\/a>, a summary of the church\u2019s teachings, states that the \u201cuse of arms must not produce evils and disorders<\/a> graver than the evil to be eliminated.\u201d In other words, the just war tradition holds that a war is justified only if the harm it causes is proportional to the good it seeks to achieve.<\/p>\n As of April 7, 2026, more than 1,600 Iranian civilians have been killed, including more than 200 children<\/a>. An estimated 3 million<\/a> Iranians have been displaced<\/a>. Schools and health care facilities<\/a> have been destroyed.<\/p>\n Musicians perform during a concert honoring children killed in a strike on a school in Minab, Iran, in Tehran on April 6, 2026.<\/span> The disruption of oil production and trade translates into higher energy and fertilizer prices, which raise food prices<\/a> \u2013 hitting the world\u2019s poorest the hardest<\/a>.<\/p>\n Whether the costs of the Iran war are proportionate depends on which of the administration\u2019s stated aims one believes.<\/p>\n The Catholic Catechism declares war can be legitimate only if \u201call other means\u201d of putting an end to an aggressor\u2019s harms \u201chave been shown to be impractical or ineffective<\/a>.\u201d<\/p>\n Arguably, U.S. officials did not give diplomacy sufficient time to work. Days before the war began, some analysts believed that a deal was close<\/a>. Oman\u2019s foreign minister, who hosted negotiations in February, said \u201cit was a shock but not a surprise\u201d that the U.S. and Israel attacked, after peace \u201chad briefly appeared really possible<\/a>.\u201d The Guardian reported that the U.K.\u2019s national security adviser, who was also present at those February talks, expressed similar sentiments<\/a>.<\/p>\n Experts suggest that the U.S. negotiating team\u2019s lack of technical expertise<\/a> and the tight timeline<\/a> contributed to failure.<\/p>\n To be justified, the use of force must be likely to accomplish the war\u2019s aims. Ethicists debate the exact bar but agree that success must be \u201cmore likely than a mere \u2018hope,\u2019 \u2018chance,\u2019 or \u2018possibility<\/a>,\u2019\u201d as international relations scholar Frances V. Harbour put it. Limited goals are more likely to succeed than expansive ones.<\/p>\n The war has degraded Iran\u2019s nuclear and missile programs<\/a>. But the knowledge needed to build them remains, and without a diplomatic solution, Iran is likely to continue its efforts<\/a> to develop such technologies.<\/p>\n Similarly, force can disrupt Iran\u2019s proxy networks and raise the costs of maintaining them, but regional diplomacy and cooperation<\/a> have a better chance of resolving such long-running concerns.<\/p>\n Ultimately, I believe a lack of clarity about the war\u2019s goals diminishes the likelihood of success. Wars require more than military victories; there must be a coherent plan for ending the fighting such that a \u201cbetter peace\u201d is established<\/a>.<\/p>\n (Valerie Morkevi\u010dius, Associate Professor, Political Science, Colgate University. The views expressed in this commentary do not necessarily reflect those of Religion News Service.)<\/em><\/p>\n \n <\/div>\n1. Legitimate authority<\/h2>\n
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AP Photo\/Mark Schiefelbein, File<\/a><\/span><\/p>\n<\/div>\n2. Just cause<\/h2>\n
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AP Photo\/Hassan Ammar<\/a><\/span><\/p>\n<\/div>\n3. Right intent<\/h2>\n
4. Proportionality<\/h2>\n
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AP Photo\/Francisco Seco<\/a><\/span><\/p>\n<\/div>\n5. Last resort<\/h2>\n
6. Likelihood of success<\/h2>\n
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