By Kelsey Davenport
By Daryl G. Kimball
Prepared Remarks by Daryl G. Kimball on the "Use of AI in Nuclear Weapon Systems: From Strategic Instability to Arms Control and Disarmament" at the Global Nobel Laureates Assembly on Artificial Intelligence and Nuclear War, Castel Gandolfo, July 14, 2026
"Asserting Human Control to Reduce the Dangers of AI and Nuclear War"
Daryl G. Kimball, Executive Director
Prepared Remarks on the "Use of AI in Nuclear Weapon Systems: From Strategic Instability to Arms Control and Disarmament" at the Global Nobel Laureates Assembly on Artificial Intelligence and Nuclear War
Castel Gandolfo, Italy, July 14, 2026
Thank you to the organizers of this august assembly and to our hosts. It is an honor to join this important dialogue at this pivotal time in human history.
As the mission statement for this conference aptly notes: the great challenges of the twenty-first century --- including Artificial Intelligence (AI) and Nuclear Weapons -- can no longer be understood or governed in isolation.
AI integration in nuclear weapons operations is occurring at the same time we face a complex and growing array of nuclear weapons-related dangers.
Tensions between nuclear-armed states are on the rise. A qualitative nuclear arms race is already underway. The world’s nine nuclear-armed actors are squandering hundreds of billions of dollars to maintain and upgrade, and in the case of China, expand the size of their deadly arsenals.
Key agreements that have helped reduce nuclear danger -- so-called guardrails against nuclear catastrophe -- are gone or at risk due to inattention or incompetence. The last treaty capping the size of the two largest arsenals (New START) expired earlier this year.
Without new restraints, we could see the U.S. and Russia increase the size of their arsenals for the first time in decades, which could trigger an unconstrained global nuclear arms race.
More nuclear weapons will not make anyone, anywhere, safer. Each of the world’s nuclear-armed states have more than enough nuclear weapons to meet their subjective requirements for nuclear deterrence and to produce destruction on a global scale.
Meanwhile, some nuclear-armed states are once again threatening nuclear use to try to coerce and bully nonnuclear states.
In sum, the risk of nuclear war is greater than at any point since the end of the Cold War. Exacerbating these challenges and the risk of nuclear war is the rush to develop autonomous weapons and the integration of artificial intelligence into interconnected nuclear command, control, and communications systems (NC3), and possibly nuclear targeting.
AI integration in nuclear operations creates new uncertainties that will likely increase the risk of miscalculation due to the loss of effective human control over decisions involving the use of the world's most dangerous weapons.
Immediate and decisive action is required to counter these growing nuclear dangers before it is too late.
The Dangers of AI in Nuclear Weapons Systems
There is a growing body of research and scholarship that strongly suggests that unconstrained introduction of AI into nuclear weapons operations (command, control, communications, as well as nuclear planning and decision-making) will lead to greater nuclear instability and increase the risk of nuclear war.
Referring to both nuclear and conventional combat operations, the 2021 U.S. National Security Commission on Artificial Intelligence, predicted that “AI will make the process of finding and hitting targets of military value faster and more efficient.”1
“Currently, this process generally involves passing data in a serial fashion from a sensor and through a series of humans, to a platform that can shoot at the target. AI will help automate some of the intermediate stages of the decision process.” As AI matures, it will propel “more advanced processes that would operate more akin to a web, fusing multiple sensors and platforms to manage complex data flows and transmitting actionable information to human operators and machines across all [combat] domains,” the report added.
In October 2024, the commander of U.S. nuclear forces said, “Advanced AI and robust data analytics capabilities provide decision advantage and improve our deterrence posture.” He called out the potential “for more effective integration of conventional and nuclear capabilities.”2
The current commander said in March this year, “Pursuant to the [Department of War’s] initiative to cultivate an “AI-first” workforce, AI and ML are now integral to USSTRATCOM’s mission, enabling the analysis and interpretation of vast data streams.”3
These and other developments create several serious risks:
Such unpredictability cannot be tolerated in nuclear operations. We are already vulnerable to potentially irrational behavior from the handful of humans who ostensibly have the sole authority to order the use of nuclear weapons; we cannot allow computer hallucinations to complicate the equation.
Inadequate Responses to the AI-Nuclear Weapons Nexus
As the major nuclear-armed states, including the United States, move rapidly to integrate AI tools across the nuclear and conventional military systems and machinery, our political, diplomatic, and legislative responses to regulate these technologies are failing to keep pace.
The best we have is the growing international consensus that artificial intelligence (AI) must never supplant human judgment in the authorization or execution of nuclear weapon launches.5
The "human in the loop" principle, while necessary, is clearly insufficient to prevent all conceivable categories of accidents that could arise from AI integration in nuclear command, control, communications, and possibly nuclear targeting.
So far, other national and multilateral efforts to establish rules of the road and/or legally-binding restrictions on AI uses in the military domain have fallen well short of what is necessary to address the risk of AI in nuclear operations.
Furthermore, the major nuclear weapon states have, so far, failed to engage in sustained bilateral or multilateral discussions with one another on how they each plan to put the "human in the loop" principle into operational practice.
The world's major military powers have generally resisted efforts to negotiate legally-binding measures -- as many states have called for and as recommended by UN Secretary General Guterres -- to ensure that autonomous weapons and AI integration in military operations are consistent with the Law of War and International Humanitarian Law.
Instead, the United States and its allies have favored the adoption of voluntary guidelines through a "Political Declaration on the Responsible Military Use of Artificial Intelligence and Autonomy," first launched in 2023.
However, that effort dropped references to AI and nuclear weapons and human control. Diplomatic efforts to advance these principles have stalled under the second Trump administration, which is seeking to accelerate the adoption of autonomous weapons and AI in U.S. military operations.
Other multilateral efforts, particularly the “Responsible Artificial Intelligence in the Military Domain" (REAIM) process—with summits in The Hague in 2023, Seoul in 2024, and A Coruña in 2026—have done important work. But U.S., Russian and Chinese support is lacking and the wide scope of the discussions -- spanning AI safety, innovation, autonomous weapons, and more -- limit their ability to address the troublesome implications of AI in nuclear weapons operations.
Recent “informal exchanges” in accordance with General Assembly Resolution 80/58 of 2025, which proposed the consultation to address the risks and opportunities posed by the accelerating application of AI to military targeting and decision-making tools, have been similarly inconclusive.
The Nuclear Disarmament Deficit
For more than a decade, progress on disarmament diplomacy that could lead to new forms of restraint has stalled due to inattention, infighting and intransigence among major nuclear-armed states.
Earlier this year, the 2026 Review Conference for the Nuclear Nonproliferation Treaty (NPT) ended without reaching a consensus outcome or action plan for the third straight time. The NPT’s nuclear five methodically forced the removal of any passages that would have committed them to begin “negotiations on disarmament” or even simply to pursue discussions on an “urgent” basis.
Instead, the final draft outcome document vaguely “calls on the nuclear-weapon States to engage in … constructive dialogue on the basis of mutual respect … and notes that such engagement could facilitate future arms control discussions, and help progress towards nuclear disarmament”
The exchanges at the conference also revealed the discord among the nuclear five on how and whether to reduce nuclear risks and nuclear arsenals.
The U.S. delegation sought to focus attention on China’s nuclear buildup and claimed it had proposed “multilateral strategic stability talks” on “transparency, risk reduction, and nuclear testing.”
However, given the vagueness of the U.S. offer and the complexities of a five-sided negotiation involving states with different force sizes, force structures, nuclear postures, and strategic cultures, this could be a formula for further inaction on disarmament.
Multilateral negotiations on disarmament involving all five nuclear-armed NPT states, if launched, might produce meaningful results.
But such an initiative should not be allowed to substitute for the immediate commencement of serious bilateral talks between the United States and Russia and the United States and China on nuclear risk reduction, strategic stability, and nuclear arms reductions that could also yield concrete arms control and risk reduction outcomes, and perhaps more quickly.
To improve the chances of success in future arms reduction talks, whether multilateral or bilateral or both, and to prevent unconstrained nuclear competition, all five NPT-recognized nuclear-armed states should agree to a mutual and verifiable freeze of their strategic launchers at their current numbers.6
This first step could reduce tensions and improve the environment for sustained talks on concrete nuclear risk reduction measures, including understandings that mitigate the risk of AI in nuclear operations, and on disarmament.
Moving Beyond the "Human In the Loop" and Reversing the Nuclear Arms Race
The situation requires urgent action in the pursuit of a new, human-centered paradigm of peace and cooperative security.
First, we must recognize the limitations and risks of nuclear deterrence and the destabilizing effects that AI integration into nuclear systems and nonnuclear military systems may create.
Nuclear deterrence requires the capability to impose unacceptable costs and the resolve to use nuclear weapons. Without the belief in this resolve, nuclear deterrence theory does not work. Deterrence proponents argue that to deter nuclear attack, one must constantly strive to make the threat of nuclear weapons use more credible in all possible scenarios.
By this logic, nuclear-armed states must develop "more usable battlefield nuclear weapons" to fill every perceived deterrence "gap”, engage in exercises to wage and win a "limited" nuclear war, and from time to time make implied or explicit nuclear threats against adversaries in crisis situations.
In other words, nuclear deterrence is a scheme for making war less probable by making nuclear war more probable.
The reality is that when nuclear deterrence fails it will fail catastrophically. If and when nuclear weapons are used in a conflict involving another nuclear-armed adversary, there is no guarantee it will not result in all-out global thermonuclear war.
Pope Leo is correct when he calls out “the widespread yet erroneous belief that nuclear deterrence is an indispensable prerequisite for security” in Paragraph 194 of his new encyclical Manifica Humanitas.
AI introduces new uncertainties to the already uncertain deterrence equation.
Second, we must demand urgent action on concrete steps that:
Regarding the use of AI for nuclear and conventional military purposes, we need enforceable and clear prohibitions that ensure meaningful human control, accountability, and democratic oversight.
Changeable national policies and executive orders are inadequate. The men who lead the small number of powerful companies who are profiting from the drive for AI innovation and implementation cannot be counted on, though they have a moral responsibility to be part of the solution.7
This requires new national legislation, effective regulation, and new international agreements and understandings. Some options include:
To address the growing danger of nuclear war and nuclear arms racing, we need serious sustained disarmament diplomacy. Tensions between the major powers are no excuse for further inaction.
If we are to hold the increasingly multipolar world together and prevent it from sliding toward nuclear chaos, we must strengthen and rejuvenate the indispensable but beleaguered global nonproliferation and disarmament enterprise, avert a new nuclear arms race, jumpstart dialogue and diplomacy between the major powers on nuclear disarmament and the destabilizing effects of AI.
Thank you for your attention.9
Download the statement (in MS Word) here.
______________
ENDNOTES
1. National Security Commission on Artificial Security (NSCAI), Final Report, 2021, p. 80, https://www.nscai.gov/wp-content/uploads/2021/03/Full-Report-Digital-1.pdf
2. Carley Welch, “AI has role to play in protecting American nuclear C2 systems: STRATCOM head,” Breaking Defense, Oct. 28, 2024, https://breakingdefense.com/2024/10/america-needs-ai-in-its-nuclear-c2-systems-to-stay-ahead-of-adversaries-stratcom-head/
3. “Statement of Richard A. Correll, Commander, U.S. Strategic Command before the House Armed Services Committee on Strategic Forces,” March 17, 2026, https://armedservices.house.gov/uploadedfiles/2026usstratcomcongressionalposturestatement2026.pdf
4. Artificial Intelligence and Nuclear Command and Control: It’s Even More Complicated Than You Think, Arms Control Today, September 2025, by Lt. Gen. John "Jack" N.T. Shanahan.
5. For example, see the 2022 working paper for the UN First Committee titled "The Principles and responsible practices for Nuclear Weapon States," submitted by France, the United Kingdom, and the United States that declares that “Consistent with long-standing policy, we will maintain human control and involvement for all actions critical to informing and executing sovereign decisions concerning nuclear weapons employment;" the original 2023 draft of the State Department’s "Political Declaration on Responsible Military Use of Artificial Intelligence and Autonomy," which proposed that governments “should maintain human control and involvement for all actions critical to informing and executing sovereign decisions concerning nuclear weapons employment.” (the current published versions does not contain such language); the respective read-outs from the November 16, 2024 meeting between Presidents Biden and Xi, which reported that "The two leaders affirmed the need to maintain human control over the decision to use nuclear weapons" and "also stressed the need to consider carefully the potential risks and develop AI technology in the military field in a prudent and responsible manner;" the 2024 U.S. Congressional legislation that stated that it is U.S. policy to ensure that AI integration does not compromise “the principle of requiring positive human actions in execution of decisions by the President;” the Russian Federation's May of 2026 report on national implementation for the NPT Review Conference, which said: "Overall, the Russian Federation ensures, on an ongoing basis, that human involvement and judgment play a decisive role in the field of nuclear weapons, including strict oversight at the level of the country’s highest military and political leadership. Against the backdrop of technological progress, this approach remains an immutable constant; " and the national implementation report of the United States for the NPT Review Conference, which declared it would "Retain – in all cases – a human "in the loop" for informing and executing the President’s decisions to initiate or terminate nuclear weapons employment."
6. As of now, Russia and the United States each have fewer than 800 total strategic launchers; China has an estimated 550, including unfilled strategic missile silos; and France and the United Kingdom have a combined total of about 96. A freeze on strategic nuclear launchers at these levels would not adversely affect any one country’s ability to deter nuclear attack, and could be more easily verified through remote, national means of intelligence.
7. See: "Want to prevent nuclear war caused by AI? Count the private sector out," commentary by Oliver Meier, European Leadership Network, July 8, 2026.
8. This builds on a concept in UN General Assembly Resolution (A/RES/80/23) on "Possible risks of the integration of artificial intelligence into command, control and communications systems of nuclear weapons," adopted on Dec. 1, 2025, which "urges those nuclear weapon States that have not yet done so, to adopt and publish national policies and doctrines explicitly affirming and operationalizing that command, control and communications systems of nuclear weapons that integrate artificial intelligence will remain subject to human control and oversight and that such systems will not autonomously initiate decisions on the use of nuclear weapons."
9. I want to acknowledge the invaluable research and analysis of my Arms Control Association colleagues Xiaodon Liang, Senior Policy Analyst and project coordinator for our AI and nuclear "firebreaks project, and our Senior Fellow, Michael Klare, which very much informed and helped to improve this presentation.
Leo XIV goes beyond calls for AI regulation and safety and says that any technological advancement detatched from ethics and human responsibilities exacerbate conflict instead of building a just peace.
July/August 2026
By Maryann Cusimano Love
Pope Leo XIV calls for disarming artificial intelligence in his recent encyclical, Magnifica Humanitas. Although the U.S. government has largely abdicated a role in establishing AI safeguards, Leo issues a rallying cry. Civil society, citizens, AI builders, governments, and multilateral organizations should not leave pivotal decisions to the tech elites alone, he argues. Instead, he calls for everyone to play a role in building peace, protecting the vulnerable, and safeguarding the treasures of human relations from digital slavery.
The encyclical is an historic first: the first encyclical of Leo’s papacy, the first written by an American, the first by a mathematician, the first written in English, and the first focused extensively on AI. An encyclical is one of the highest forms of teaching in the Roman Catholic Church. It was addressed not only to the 1.4 billion Catholics who comprise the largest branch of Christianity, the world’s largest religion, but to everyone with the aim of advancing discussion and dialogue about urgent moral issues.
A New Long-Term Project
The Catholic Church is well-practiced in undertaking long-term building projects. The Milan Cathedral took nearly six centuries to complete. Leo just blessed the Sagrada Familia Basilica in Barcelona, after nearly a century and a half of construction, interrupted by the Spanish Civil War, World War II, and the COVID-19 pandemic. Hence, it is natural that Leo opens the encyclical with two contrasting building images that he returns to throughout the text: the negative example of building the Tower of Babel, a hubristic technological ascent, versus the positive example of the decentralized rebuilding of Jerusalem, a slower community construction project. He urges his readers to avoid “the Babel syndrome,” meaning an “idolatry of profit that sacrifices the weak,” and the dehumanization of reducing persons into data, performance, and targets to exploit. Instead, he advocates that people build together for the common good and assures that even if construction moves at a slower pace, a better result awaits.1
In an unprecedented move, Leo spoke publicly about the encyclical when it was unveiled May 25, saying, “artificial intelligence needs to be disarmed. The word is strong, I know, but deliberately chosen.… The church has long been working for nuclear disarmament, aware that every great technical power can affect people’s lives and so must be accompanied by adequate moral discernment and public control. Nuclear disarmament remains a service to peace and the dignity of the human family.”2
He continued, “In a similar sense, artificial intelligence now demands to be ‘disarmed,’ freed from logics that turn it into an instrument of domination, exclusion and death. Like nuclear energy, it must be at the service of all and of the common good. Decisions about technology must never be separated from conscience and responsibility.… vigilance is necessary today. Peace, not merely the absence of war, is justice at work. But when technology weakens our critical sense, peace itself is at risk. Disarming, however, is not enough. We must build.… a future, not for a privileged few, but for the entire human family.”3
The encyclical is a broad and deep analysis of what it means to be human in a digital age, warning about advancing technology without a moral compass and the concentration of power in the hands of a select few tech elites. Leo underscores that “technology is never neutral, because it takes on the characteristics of those who devise, finance, regulate and use it.”4 He notes the good that AI and emerging technologies can do in fields such as medicine, for example, but he also warns of the risks of technology being used to dominate, dehumanize, and exploit in pursuit of power and profit rather than the common good.
The encyclical peels back deeper layers beyond the usual policy questions over AI regulation and governance. Who are we and who do we want to be? What do we want to build to serve humanity? How can we build ethically, caring for one another and our common home? Leo contests the vision and building plans of some AI elites, such as Elon Musk, that view humans as merely the small bit of code and “biological boot loader” used to create superior machine intelligence.5 He covers the impact of AI on the environment, education, families, employment, human trafficking, truth and democracy, and of war and peace.
Why Listen to the Church?
Some tech powers in Silicon Valley welcomed Leo’s decision to open the conversation on the ethical concerns surrounding AI, which has become integral to war-fighting and national security decision-making. Christopher Olah, a co-founder of Anthropic, regularly consults Catholic thinkers on the ethics (or as he refers to it, the “soul”) of Claude and other Anthropic products; he participated in the release of the encyclical at the Vatican. Anthropic’s CEO, Dario Amadei, agrees with Leo that AI leaders such as himself should not be deciding the future of these technologies on their own.6
Others in Silicon Valley are pushing back, arguing that the pope should stay in his lane, and that the Catholic Church is not competent to discuss AI.7 Leo is a mathematician who leads the world’s largest nongovernmental educational network, including over 1,400 universities, 230,000 schools and educational institutions, academic institutes and think tanks on artificial intelligence and emerging technologies in almost all countries. They include The Catholic University of America’s Leonine Institute for Emerging Technologies and the University of Notre Dame’s DELTA network. Catholic professors, such as I, have degrees in AI and teach AI courses and programs. Catholics build and use AI programs, and Holy See diplomats negotiate on AI law and policy. Many Catholic priests, who are also scientists and engineers, serve as AI advisers to governments and international bodies, including the United Nations and European Union, and to the tech industry.
The Holy See led the Rome Call for AI Ethics, a pledge pioneering the development and application of common principles for AI ethics and regulation, including accountability, inclusiveness, impartiality, and privacy. Major tech companies such as Microsoft, IBM, Cisco, and Salesforce are signatories. The Pontifical Academy of Sciences traces its lineage from one of the oldest scientific forums in history, the Accademia dei Lincei (1603-1651), which counted Galileo Galilei among its members. Many Nobel laureates are members, and AI has been a dialogue theme between religious and scientific leaders for many years now.
Nobel laureates and Catholic experts met July 14-16, 2025, in Rome for a discussion of AI and nuclear weapons. For more than a decade, long before the advent of ChatGPT and today’s large language models, the Catholic Church has been convening the Minerva Dialogues between AI industry leaders and religious leaders, urging that AI respect human dignity and serve the common good. Two Church offices, called dicasteries, released Antiqua et Nova: Note on the Relationship Between Artificial Intelligence and Human Intelligence last year. Leo’s Magnifica Humanitas encyclical is not a one-off; it is the fruit of this long engagement and discernment on these issues.
Realist thinkers argue that religious actors and factors have no role in international relations or should have no role,8 but this assertion rather proves the point that the pope is making about the need to overcome a culture of exclusion. It is not merely a matter of creating more moral machines. “A more moral AI is not enough if that morality is determined by a few,” Leo wrote.9
Unlike the frontier AI companies, the Catholic Church is not selling AI, so it can speak frankly. The tech titans have a conflict of interest in promoting their lucrative interests while claiming there are no serious downsides to their products, tech companies can be trusted to self-regulate, yet resisting attempts to strengthen requirements for transparency, accountability, safety regulations, and guardrails. Palantir co-founder Peter Thiel—a self-identified libertarian, conservative Christian, MAGA contrarian—seems to be trolling Pope Leo. In a series of lectures held in Rome near the Vatican, Thiel claimed that those who propose AI regulations are the Antichrist.
Disarming AI
Leo goes beyond calls for AI regulation and safety. He urges deeper relationships for deeper disarmament and says that any technological advancements detached from ethics and human responsibilities exacerbate, accelerate, and dehumanize conflict, cyberattacks, and hybrid war, rather than building just peace. “Disarming AI means freeing it from the mentality of ‘armed’ competition, which today is not limited simply to the military context, but is also an economic and cognitive phenomenon. This entails a race for ever more powerful algorithms and larger datasets, driven by the desire to secure geopolitical or commercial dominance,” he writes.10
Leo continues: “To disarm means discrediting the assumption that technical power automatically confers the right to govern. To disarm does not mean rejecting technology but preventing it from dominating humanity. It means freeing technology from monopolistic control and opening it to discussion and debate, therefore making it human-friendly and restoring it to the plurality of human cultures and ways of life.… For this reason, merely regulating it is insufficient; it must be disarmed, welcoming and accessible.”11
In this context, the pope says that disarming AI means confronting realpolitik, the culture of power that normalizes war under a false realist school of international relations theory that incorrectly claims conflict is inevitable, so therefore arm up. By erasing truth and the historical memory of the harms and horrors of war, algorithms and communications networks reward conflict and stoke disinformation and fear while sanitizing and gamifying violence.
In the encyclical, Leo expands upon previous Catholic calls against lethal autonomous weapons systems and in favor of nuclear disarmament and arms control. He notes that “No algorithm can make war morally acceptable,”12 and sets out three non-negotiable requirements for the use of AI in military systems. First, the buck must stop with a person; accountability and blame cannot be “collapsed into ‘the machine,’” but must be traceable to human decision-making processes. Second, the use of force must “remain under effective, self-aware and responsible human control.” And third, at the communal level, the world must develop a shared international framework to curb the AI and technological arms race.13
Leo further makes the point that words are powerful and must be chosen wisely to favor more peaceful, less aggressive language over confrontational language that divides humanity into in-groups and out-groups.” He urges people to disarm hearts, words and relationships, in order to build a just peace and move away from the normalization of war, the arms race, the false logic of deterrence, and the just war tradition.
Just Peace Over Just War
In repudiating the normalization of war, Leo criticizes just war theory as outdated. Some media outlets jumped on this quote and reported that the pope had overturned just war tradition. Not exactly.
The just peace tradition is the majority position within the church and holds that the objective at all times is to prevent conflict, end conflict, and build peace. The just war tradition is the minority position.14 Popes have emphasized the just peace tradition for decades, while de-emphasizing the just war tradition. Leo clears up several common errors. First, he says that Jesus worked to build a just peace without violence. The just war tradition was never the foundational Catholic teaching on war and peace. It emerged centuries later to limit violence, not to justify or expand war, as it is commonly misunderstood today.
Second, Leo notes that St. Augustine has been stripped of his original emphasis on building a just peace and turned into a caricature as a proponent of war. An example is when Vance tried to invoke Augustine to justify the U.S. attacks on Iran—Leo is not having this. Throughout the encyclical, he writes that the Catholic tradition seeks to build a just peace, while lamenting the false manipulation of the just war tradition to justify any kind of violence. Unjust wars are being fought for profit, and arms makers and the military-industrial complex fuel conflicts to reap these profits.
Leo reiterates that “preventive” attacks are not just, and do not meet the strict conditions of self-defense, nor do unjust wars fought to divert public attention from domestic problems. As the former head of the Augustinian order (Catholic religious orders are often named after the saints that founded or inspired them) and a scholar of St. Augustine, Leo reminds his readers that the saint put the drive for a just peace first and foremost among his priorities. “In an increasingly interdependent world, peace is not just one issue among others, but a prerequisite for the universal common good and a test of the moral maturity of peoples, especially of those who bear responsibility for governing,” he writes.15
Third, Leo notes that humanity has far more effective tools to resolve conflict, such as dialogue, diplomacy, and forgiveness, than its leaders have sought to exercise. He recommends applying all the just peace principles and practices—expanding participation in restoring communities, building right relationships, truth-telling, and reconciliation—to build a more sustainable peace with one another and with our common home. These tools are practical and have a successful record, which Leo documents: restoring and rebuilding Europe after World War II and building multilateral and international laws and institutions, such as the UN, the Universal Declaration of Human Rights, the Refugee Convention, the Treaty on the Prohibition of Nuclear Weapons, the U.S. civil rights movement, the anti-apartheid movement in South Africa, and Wangari Maathai’s Green Belt movement. With more effective tools available to build just peace, the just war doctrine is outdated.
Finally, given the immense destructive potential of modern war, Leo writes that the “evils” of war outweigh the harms that force seeks to eliminate. He does not mention the U.S.-Israeli war on Iran specifically but notes that, “It is much easier to start a war than to stop it.”16
All popes since World War II have called for a greater emphasis on building a just peace, noting that almost all conflicts do not meet the criteria for a just war. Catholic peace groups such as Pax Christi USA and Dorothy Day’s Catholic Worker call for going farther by totally eliminating the just war tradition, in the same way that the Catholic Church changed its position from supporting to opposing the death penalty. It is more likely that Leo the Augustinian will restore St. Augustine’s emphasis on just peace, rather than jettison the just war tradition entirely. He mentions “peace” 67 times in Magnifica Humanitas, and “just war” only once. He retains the narrow strict exception for self-defense, as in the case of Ukraine’s self-defense against Russian attacks, and calls for increased protections of civilians, consistent with the just war tradition’s in bello criteria.
Leo disputes that peace is utopian.17 Empirically, it is not. Most of the world is at peace, most of the time. We work to build peace in our families, workplaces, and communities. Leo is calling humanity to the construction site and telling us to bake bricks and bring them along. Building peace is a moral and religious obligation and a practical action plan.
Criticisms of Nuclear Deterrence
Some proponents of nuclear deterrence hoped Leo would overturn his predecessor’s encyclical, Fratelli Tutti, which holds that the possession of nuclear weapons and adherence to nuclear deterrence are immoral. They will be disappointed. There is no daylight between Leo’s critiques of nuclear deterrence and those of his predecessor, Pope Francis. The new encyclical calls out “the widespread yet erroneous belief that nuclear deterrence is an indispensable prerequisite for security.”18 From a just peace perspective, deterrence displays “a relational poverty that always has disastrous consequences for civilian populations,” Leo writes.19
None of the nuclear armed states are engaged in disarmament negotiations, and the Trump administration argues that this is not the time for such negotiations, that diplomacy must wait until conditions are ripe. Instead the administration prefers multilateral consultations on risk reduction and nuclear testing. Leo disputes this narrative and any assertion that there are parties with whom it is illegitimate to engage. In his view, the time is always right for disarmament negotiations, diplomacy, and dialogue. Leo invokes Fratelli Tutti, which also notes that it is immoral to possess nuclear weapons.20 Dialogue is not transactional but transformative, Leo writes. Diplomacy is a vocation, requiring abundant perseverance, humility, patience, and openness to the other.
For those who hope the Catholic Church will bless the bombs that undergird nuclear deterrence as the Russian Orthodox Church does, that is not going to happen. Not all remarks made by the pope are authoritative, binding, high-level teaching of the Catholic Church. If Leo roots for the White Sox and orders a hot dog at the game, Catholics are not bound to do the same. At the top level of Catholic teaching are apostolic constitutions (such as Vatican II), followed by encyclicals. At the end of the line are pastoral letters by just one bishops’ conference and remarks. The calls for abolishing nuclear weapons, nuclear disarmament, and the critiques of deterrence are in the constitutions and papal encyclicals of higher levels of Catholic teaching. The 1983 pastoral letter of the U.S. Catholic bishops, which in one section offered limited strictly conditional acceptance of nuclear deterrence as long as it was on the path to deeper disarmament,21 was lower-level Catholic teaching, now outdated.
Leo proposes several ways forward: disarming words by speaking the truth; building peace in justice; adopting the perspective of victims; and rejecting realpolitik and seeking practical paths of peace through deeds, diplomacy, dialogue, and multilateral cooperation. Even in the darkest nights, peacemakers build and persevere with astonishing creativity in doing good, protecting the vulnerable, and opening pathways to reconciliation. We are invited to the construction site to build a more fully human future in the digital age, and not to give up just because big tech owns the brick company.
ENDNOTES
1. Pope Leo XIV, Magnifica Humanitas, May 25, 2026, paragraph 10. All following quotes from Magnifica Humanitas include just the paragraph number in brackets.
2. Pope Leo, Remarks at the public event releasing Magnifica Humanitas, May 25, 2026, Vatican City.
4. Magnifica Humanitas, paragraph 9.
5. Elon Musk, “Hope we’re not just the biological boot loader for digital superintelligence. Unfortunately, that is increasingly probable,” Twitter, August 3, 2014.
6. Elias Wachtel, “Why Silicon Valley is Turning to the Catholic Church,” The Atlantic, April 25, 2026.
7. Cade Metz, “At the Epicenter of A.I., Pope Leo’s Warnings Are Dismissed,” The New York Times, May 26, 2026.
8. Maryann Cusimano Love, Global Issues Beyond Sovereignty, Chapter Five, “Religious Actors and Factors in International Politics” (Rowman & Littlefield: Lanham, MD, 2020).
9. Magnifica Humanitas, paragraph 107.
10. Magnifica Humanitas, paragraph 110.
11. Magnifica Humanitas, paragraph 110.
12. Magnifica Humanitas, paragraph 198.
13. Magnifica Humanitas, paragraph 200.
14. Maryann Cusimano Love, “Just Peace and Just War,” Expositions, Vol. 12, No. 1 (2018), pp. 60-71.
15. Magnifica Humanitas, paragraph 182.
16. Magnifica Humanitas, paragraph 195.
17. Magnifica Humanitas, paragraph 205.
18. Magnifica Humanitas, paragraph 194.
19. Magnifica Humanitas, paragraph 192.
20. Maryann Cusimano Love in Chris Seiple and Dennis R. Hoover (eds.), Routledge Handbook of Religious Literacy, Pluralism, and Global Engagement, Chapter Four, “Fratelli Tutti: Lessons Learned from Interreligious Action and the Catholic Church” (Taylor & Francis, 2021).
21. U.S. Conference of Catholic Bishops, “The Challenge of Peace: God’s Promise and Our Response” pastoral letter, May 3, 1983.
