The Vatican’s Nuclear Diplomacy from the Cold War to the Present


In June 1982, Pope John Paul II broke with over three decades of Vatican policy when he emphatically stated in front of the United Nations General Assembly that nuclear deterrence could be judged as “a morally acceptable step on the way toward a progressive disarmament.” This statement stood in marked contrast to his predecessors, who rejected peace based on the threat of mutual annihilation. Since the beginning of the nuclear age, the Vatican has placed nuclear issues at the top of its foreign policy agenda. Though the Cold War superpowers were very concerned with the Vatican’s position on nuclear arms, it has, nevertheless, received little scholarly attention in historical analyses of the arms race. For example, when President Ronald Reagan decided to pursue his Strategic Defense Initiative — a controversial missile defense system — to “render nuclear weapons impotent and obsolete,” he actively sought the pope’s support. Meanwhile, the Soviet Union lobbied, unsuccessfully, to get John Paul II to publicly condemn the program. In the 1980s, the Pontifical Academy of Sciences in Vatican City became a forum for scientists from both sides of the Iron Curtain to exchange ideas on nuclear issues.



In the post-Cold War era, the Vatican remains very active in its effort to influence the international dialogue on nuclear weapons. Pope Francis has made nuclear arms control a primary objective of his foreign policy. He has changed course from John Paul II’s position on deterrence and stated that not only the use, but also the possession of nuclear weapons is immoral. In addition to advocating comprehensive arms reduction agreements, Pope Francis is committed to raising awareness about the potentially destabilizing effects of artificial intelligence on the future of warfare, including nuclear stability. The pope no longer has a large military at his disposal, nor significant economic resources. The Vatican does, however, have diplomatic relations with 183 countries in addition to its international moral authority. From the Cold War to the present time the Vatican has been a significant but understudied player in international deliberations on nuclear weapons and disarmament.

The Vatican Enters the Nuclear Age

Throughout the Cold War, the Pontifical Academy of Sciences served as the main forum for the Vatican’s scientific and moral debates regarding nuclear weapons. It has served to inform the nuclear diplomacy of the Vatican from the dawn of the nuclear age until the present time. Pius XI founded the modern academy in 1936, but it can trace its lineage back to the 16th century and even had Galileo as one of its members. Pius XI wanted to establish a forum for dialogue between faith and science in the modern age, and appointed over eighty academicians from many different countries. Notably, since its founding, members of the academy do not have to be Catholic or have any religious affiliation. The academy has had more than forty Nobel laureates — Max Planck, Werner Heisenberg, and Niels Bohr were just three of the many prominent 20th century scientists who were elected members of the Pontifical Academy of Sciences. Pius XI believed that the search for truth was the primary objective of the academy. This goal would have significant political repercussions when the academy began examining the morality of nuclear weapons in the coming decades.

In March 1939, Cardinal Eugenio Pacelli was elected by his peers to become the Supreme Pontiff of the Roman Catholic Church. He chose Pius XII as his regnal name. Like his predecessor and mentor Pius XI, he was a seasoned papal diplomat and intimately understood the political landscape of Europe. He was profoundly anti-communist and believed that cooperation with and accommodation of the Soviet regime was not only inadvisable, but indeed also impossible. He remained in Rome during World War II and witnessed first-hand the devastation wrought by allied strategic bombing. What he is perhaps least recognized for is his intense interest in the scientific and technological changes taking place in the 1930s and 1940s.

Pius XII was especially concerned with developments in atomic research during this period. He had extensive contact with German physicist Max Planck about the potential consequences of nuclear power for warfare. In 1941, the pope told a gathering of the Pontifical Academy of Sciences that in the hands of man, science can become a double-edged weapon capable both of curing and killing. At the urging of Planck, in 1943 the pope said that scientists were informing him that nuclear technology could create “an amount of energy that could take the place of all the largest electrical power plants in the world.” He warned, however, that such technology should only be used for peaceful purposes “because otherwise the consequences would be catastrophic… for the whole planet.” The pope became distraught when he learned that the United States used atomic bombs on Hiroshima and Nagasaki. He described nuclear weapons as “the most terrible weapon that the human mind has ever conceived.”

Pius XII did, however, maintain that the use of force could be justified in a modern context. In 1953 he said, “It is certain that even in the present-day circumstances war cannot be considered illicit for a nation to efficiently defend itself and to achieve victory when it is attacked unjustly and all efforts to avoid it have proved futile.” He did declare, nevertheless, that nuclear weapons could not be employed within the boundaries outlined by St. Augustine’s writings on just war theory — this body of work guided the Vatican’s position on war.

In the 5th century, St. Augustine claimed that defense could be a necessity when justified by a legitimate authority and that “the wise man will wage just wars.” Nine hundred years after St. Augustine, St. Thomas Aquinas expanded on the former’s writings about conflict and stated that war must occur for a good and just purpose, that war must be waged by a properly instituted authority (e.g. a state), and that peace must be the central motive. Pius XII specifically identified Aquinas’s condition of “peace as a central motive” as a primary problem with the use of nuclear weapons. He stated that “when the harm wrought by war is not comparable to that caused by tolerating injustice, we may be obliged to suffer injustice.” For the pope, because nuclear weapons would likely kill so many non-combatants, they could never be employed within the just war theory framework outlined by Augustine and Aquinas.

Pius XII used scientific arguments against the testing and deployment of nuclear weapons. More specifically, he focused on the potential effects of nuclear fallout as a compelling reason why nuclear weapons should never be used. He used his Christmas message in 1955 to articulate the harmful effects of nuclear testing and the use of atomic weapons, saying, “a nuclear explosion releases an enormous amount of energy… in an extremely short period; it consists of radiations of an electromagnetic nature of very high density… launched at speeds close to that of light… wreaking havoc.” Thus, he emphasized the use of science — in addition to moral imperative — as a rhetorical weapon in his passionate arguments against the possession and use of atomic weapons.

In October 1958, Pius XII died and was succeeded by John XXIII, who was also a seasoned papal diplomat. Like his predecessor, he was very concerned with the threat of nuclear war. A little over one year after the Cuban Missile Crisis, on April 11, 1963 he issued his encyclical Pacem in Terris (“Peace on Earth”). In it, he acknowledged that nuclear weapons could “indeed act as a deterrent” but he also stated that “the very testing of nuclear devices for war purposes can… lead to serious danger…” He also rejected the idea of peace based upon mutually assured destruction, observing that, “lasting peace among nations cannot consist in the possession of an equal supply of armaments, but only in mutual trust.” In addition, he expressed grave concerns about the economic costs of the nuclear arms race.

John XXIII emphatically rejected the idea that nuclear weapons could be justified on moral grounds when he said “in this age which boasts of its atomic power, it no longer makes sense to maintain that war is a fit instrument with which to repair the violation of justice.” He did, however, break with Pius XII’s vocal anti-communism. He wanted to lower the overall tension between east and west. So, while he maintained that nuclear weapons were not acceptable, he did reduce the Vatican’s direct moral and political pressure placed on the communist world in particular.

In 1963, John XXIII died and was succeeded by Paul VI, who carried on his predecessor’s legacy on nuclear weapons. He stated that peace created by nuclear deterrence was “a tragic illusion.” Most significantly, he instituted the Vatican’s policy of Ostpolitik (“Eastern Politics”) aimed at rapprochement with the Soviet Union. He believed that the USSR could last indefinitely and that it was better to seek a peaceful accommodation than to maintain a policy of hostility and isolation. This policy represented a complete departure from Pius XII’s vocal anti-communism. In 1978, Paul VI passed away and was replaced by John Paul I. His papacy lasted for only 33 days, and thus he did not make any significant foreign policy changes. His successor would, however, lead the Vatican in a completely new direction and change the course of the Cold War in the process.

A New Pope Accepts Deterrence

When Cardinal Karol Wojtyla became Pope John Paul II in 1978, he was the first non-Italian pope in over 400 years. The election of a Polish pope during this tense period in the Cold War immediately drew the attention of the Soviets. The KGB and its Polish sister service had been closely following the career of the man who would be John Paul II for many years. After he became pope, the Kremlin was intensely concerned with his diplomatic agenda. According to Vatican scholar George Weigel, John Paul II rejected Ostpolitik and he pursued “a strategy of resistance through moral revolution.” In 1981, he visited Hiroshima and Nagasaki and spoke about how the arms race was getting out of control and placing the future of humanity in jeopardy. In June 1982, he stated in front of the United Nations General Assembly that nuclear deterrence could indeed be judged as a moral intermediate step toward disarmament. He continued, nevertheless, to encourage world leaders to push for arms reduction.

When Reagan became president in 1981, he very much saw John Paul II’s position on communism and nuclear weapons as in line with his own. He abhorred nuclear weapons and wanted to find a way out of the arms race. During his presidency, questions about the morality of nuclear strategy became a central point of concern. Adm. James Watkins, Reagan’s Chief of Naval Operations, was a devout Catholic and stated openly in 1983 that mutually assured destruction was not a morally sound long-term strategy. In 1983, the Reagan administration was deeply disturbed by the United States Conference of Catholic Bishops’ report on nuclear weapons that also questioned the morality of mutually assured destruction. In light of the significant doubts about the morality of American national strategy, Reagan sought the pope’s support for his plan to change the nature of the American-Soviet arms competition.

In March 1983, Reagan announced his intention to create a capability that would render nuclear weapons obsolete and move the world out from under the threat of mutually assured destruction, a vision that ultimately became the Strategic Defense Initiative. Reagan sought out the Vatican’s support for this program. A declassified Central Intelligence Agency memorandum details a January 1986 trip of a Strategic Defense Initiative briefing team to the Vatican. Members of this group provided senior Vatican officials and scientists from the Vatican observatory a briefing on the program. Multiple high-ranking clerics informed the U.S. ambassador to the Vatican that “it would be impossible for them to support a military program, which potentially takes food from the mouths of the poor.”

While Pope John Paul II did not overtly support missile defense, he refused to criticize it either. Many Pontifical Academy of Sciences members believed that the program could have negative repercussions for the arms race. The pope was very concerned about the implications of emerging technologies for superpower relations. In the early and mid-1980s, the academy hosted conferences on nuclear security issues that drew distinguished scientists such as American physicist and national security expert Richard Garwin and Soviet physicist Evgeny Velikhov. In 1985, the academy began compiling a report on the implications of the Strategic Defense Initiative for strategic stability. When the Reagan administration discovered this, it began lobbying the Vatican not to publish the report. At the same time, the Soviet foreign minister flew to Vatican City and tried to convince the pope to publicly criticize the program. John Paul II, however, in no way wanted to appear to be supporting a Soviet cause. In the end, the pope ensured that the report was never published. While both superpowers were in a race over strategic technology, they were also competing for the support of the Supreme Pontiff of the Roman Catholic Church.

Vatican Nuclear Diplomacy after the Cold War

On April 19, 2005 German Cardinal Joseph Ratzinger succeeded John Paul II and became Pope Benedict XVI. He was the first post-Cold War pontiff. Even though the Cold War was officially over, he remained intimately concerned with nuclear proliferation and its effects on the developing world in particular. Benedict XVI was especially worried about “how expenditure on armaments served to perpetuate domestic and local inequalities” and he emphasized the “urgent need to both revitalize non-proliferation efforts and move to decommission existing nuclear weapons.” In his first World Day of Peace Message in 2006 he declared that, “in a nuclear war there would be no victors, only victims.” He thus built upon the arguments of his predecessors and also emphasized the socio-economic consequences of a strategy based on nuclear deterrence. His successor would, however, go even further in his advocacy for abolishing nuclear arms.

In February 2013, Benedict XVI became the first pope since the 15th century to resign the papal office. He was succeeded by Argentine Cardinal Jorge Mario Bergoglio, who took Francis as his regnal name. Since the beginning of his papacy, Francis has made the elimination of nuclear weapons a top priority of his foreign policy. In 2015, he said in front of the United Nations General Assembly that “we must therefore commit ourselves to a world without nuclear weapons.” He condemned even the possession of nuclear weapons as immoral with his statement that “the threat of their use as well as their very possession is to be firmly condemned.” He broke, therefore, completely with John Paul II’s position that nuclear deterrence could be considered a moral intermediate step towards disarmament. Pope Francis has also put his words into action. In July 2017, the Vatican voted in favor of a treaty that prohibits the “development, testing, production, manufacture, otherwise acquisition, possession or stockpiling [of] nuclear weapons or other nuclear explosive devices.”

The current pope is also very concerned about the potentially negative implications of emerging technologies that could affect nuclear command and control. He has placed a spotlight on artificial intelligence and is worried about its likely influence on the future of warfare. In May 2019, the Pontifical Academy of Sciences hosted a conference on artificial intelligence that specifically considered its possible consequences for military operations. The implications of artificial intelligence for nuclear stability looms very large in the minds of many academy scientists who directly advise the pontiff on scientific and technological matters.

While the Vatican has placed great emphasis on working towards a world without nuclear weapons, has it had an impact? During the Cold War, Reagan certainly believed that the pope’s moral authority added significant momentum to the arms control negotiations taking place in the 1980s. In 2015, Rose Gottemoeller, President Obama’s senior arms control official in the State Department, stated, “I think there is a huge moral impact of the Vatican on issues that relate to nuclear weapons deterrence and the disarmament agenda overall” and that “you can’t just wave a magic wand and make nuclear weapons go away. It takes hard work and it takes a lot of very practical steps, but we can get there.” Obama was receptive to the pope’s message on nuclear weapons and sought to work with him towards the elimination of nuclear weapons, though no significant strides were made as a result of Washington’s and the Vatican’s shared vision.

Events of the past 75 years strongly suggest that the Vatican is unlikely to make any significant headway with its nuclear diplomacy without support from the United States. The present pope’s declaration that even the possession of nuclear weapons is immoral will likely alienate the nuclear powers and actually impede the Vatican’s objectives in the realm of nuclear diplomacy. John Paul II, by contrast, had a realist perspective on the international system, which enabled him to formulate policies that gave the Vatican a greater voice in international affairs. The alignment of Vatican and American policy on arms control began to unravel, however, in the post-Cold War era.

The Limits of Moral Authority

In the 1940s the Vatican recognized that nuclear weapons would fundamentally change the nature of the international system. Since that time, each pope has consistently lobbied against their use. The Cold War environment created a willingness among popes, John Paul II in particular, to accept nuclear deterrence. In the post-Cold War period, the Vatican has passionately condemned nuclear deterrence and made the abolition of nuclear weapons a primary foreign policy objective. World leaders recognize that the pope is the head of an institution with over one billion members. He has diplomatic relations with over 180 countries, including Russia and Iran, and has been recognized by both Moscow and Tehran as having significant influence in international relations. The United States and the Soviet Union both lobbying the Vatican to support their respective positions on the Strategic Defense Initiative strongly suggests that the moral authority of the pope is not an insignificant consideration in international affairs.

The nuclear age does, however, demonstrate that the moral authority of the papacy has significant limits. The Vatican recognizes that it cannot achieve its objective of nuclear disarmament without the agreement of all the nuclear powers, which is an outcome that is unlikely in the near future. For the past seven decades, the Vatican has persistently engaged with world leaders on shaping norms surrounding the possession and use of nuclear arms. Its policy of political non-alignment and its intellectual arguments based in the just war tradition have solidified its place among the prominent voices shaping the dialogue on nuclear issues. The reality is that hard power still supersedes the moral influence of the oldest institution in the world and moral arguments have not solved the security dilemma facing the nuclear powers.

Nevertheless, the Vatican has grown accustomed to confronting substantial political challenges over the last two millennia, so the pope is willing to wait patiently.



Aaron Bateman is pursuing a Ph.D. in the history of science and technology at Johns Hopkins University. Previously, he served as a U.S. Air Force intelligence officer. He has published on a wide variety of subjects including technology and international affairs, diplomacy, and Cold War history.

Image: Ronald Reagan Presidential Library

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