Two sentences, written seventy-three years apart, are worth setting side by side this morning. The first is from Article III of the Mutual Defense Treaty signed in Washington on October 1, 1953: each party “would act to meet the common danger in accordance with its constitutional processes.” The second went up on Truth Social Sunday afternoon: “I recently asked the President of South Korea if they would like to join us in the Denuclearization of the Islamic Republic of Iran, and they said, ‘No thanks!’” One of those sentences is a promise. The other attaches a price to it. Catholic social doctrine has a specific, unembarrassed answer about what happens when the second kind of sentence starts governing the first.

The News Story

President Donald Trump announced Sunday that he has ordered the Pentagon to substantially cut back joint military exercises with South Korea, tying the decision both to his relationship with North Korean leader Kim Jong Un and to Seoul’s refusal to assist the United States in its war with Iran. The announcement came hours before Ulchi Freedom Shield, one of the two major annual U.S.–South Korea exercises, was scheduled to begin.

In a post on Truth Social, Trump wrote: “Based on my very good relationship with Kim Jong Un, of North Korea, I am not happy with the fact that the United States has, long ago, agreed to participate in Joint Military Exercises with South Korea.” He said the exercises “are not only costly, with much of these costs paid for by the United States of America (as usual!), but send a signal that is totally inappropriate and hostile,” describing North Korea as a country that “has been unthreatening and respectful” during his presidency. Trump added that it was “too late to cancel” this year’s drills and said he had instructed Secretary of War Pete Hegseth to “substantially reduce” them.

In the same post, Trump raised a separate grievance about the Iran war. “While somewhat unrelated (?), I recently asked the President of South Korea if they would like to join us in the Denuclearization of the Islamic Republic of Iran, and they said, ‘No thanks!’” he wrote, referring to South Korean President Lee Jae Myung. He did not specify what form of cooperation he had requested. Washington has pressed allies during the conflict to send warships to the Strait of Hormuz and contribute to postwar reconstruction funding.

South Korea’s Ministry of National Defense said Monday that Ulchi Freedom Shield would “proceed as previously notified and scheduled.” The exercise began Monday and runs through August 27, involving roughly 18,000 South Korean troops in a command-post exercise and a field-training component. South Korean media reported that the number of battalion-level or larger field exercises had already been reduced from 17 last year to 14 this year; South Korea’s Joint Chiefs of Staff have characterized that change as a rescheduling rather than a scale-back. Because the exercise plan was released August 10, it remains unclear when any further reduction would take effect. Roughly 28,500 U.S. troops are stationed in South Korea.

North Korea has long denounced the drills as rehearsals for an invasion; Washington and Seoul describe them as defensive. Pyongyang conducted ballistic missile launches on August 6 and August 12, both falling into the waters between Korea and Japan, which the United States, Japan and South Korea condemned. A North Korean foreign ministry spokesperson said Friday that U.S.–Japan–South Korea military cooperation was becoming a “nuclear alliance” and that Pyongyang would answer with “a new level of deterrent.” The day before his post, Trump shared a 2019 photograph of himself with Kim, writing that the two “get along GREAT!”

Australian Lt. Gen. Scott Winter, deputy commander of U.N. Command, told reporters in Seoul last week that planners accounted for North Korea’s expanded missile program and the battlefield experience gained by as many as 14,000 North Korean troops deployed in support of Russia. Trump made similar overtures in 2018, calling the drills “provocative” after his Singapore summit with Kim. ^{[1][2][3][4][5][6][7][8][9]}

Catholic Social Teaching Analysis

Nations Are Subjects Of Reciprocal Rights And Duties

Start with the sentence that most Americans have never been told is Catholic teaching at all. John XXIII, writing in 1963 with Soviet missiles barely out of Cuba, opened his treatment of relations between states this way: nations “are the subjects of reciprocal rights and duties,” and their relationships “must likewise be harmonized in accordance with the dictates of truth, justice, willing cooperation, and freedom.” Then the line that does the real work: “The same law of nature that governs the life and conduct of individuals must also regulate the relations of political communities with one another.”^[10]

That is a much bigger claim than it looks. It means there is no separate moral universe called foreign policy. A president negotiating a treaty is under the same obligations of truth and fidelity that bind a man signing a mortgage or making a vow, and John XXIII says so explicitly a paragraph later: political leaders cannot “lay aside their natural dignity while acting in their country’s name and in its interests,” and “they have no authority to depart from its slightest precepts.”^[11] The Compendium of the Social Doctrine of the Church picks up the same point four decades on and states it as a rule: to build a peaceful international order, “the same moral law that governs the life of men must also regulate relations among States.”^[12]

So the question in front of us this morning is a question about what a promise is, asked at the scale of two governments and about 80 million people who live under the promise’s shelter. Strategy comes later, downstream. And the Church answers questions about promises with unusual precision, because she has been answering them since the confessional was invented.

Pacta Sunt Servanda Is Not A Footnote

The Compendium is the Church’s own organized summary of her social doctrine, and when it reaches the fundamental rules of the international community it produces a short list. Juridical and theological reflection, it says, has formulated “universal principles which are prior to and superior to the internal law of States”: the unity of the human race, the equal dignity of every people, the rejection of war as a means for resolving disputes, the obligation to cooperate for the common good, “and the need to be faithful to agreements undertaken (pacta sunt servanda).”^[13]

Five principles, and faithfulness to agreements is one of the five. Then the Compendium does something it rarely does, which is to rank its own list: “This last principle should be especially emphasized in order to avoid ‘temptation to appeal to the law of force rather than to the force of law.’”^[14]

That ranking explains why keeping treaties matters so much more than it seems to. Every international agreement is a substitute for coercion. Two nations who have signed something have agreed to settle a matter by words that stay fixed rather than by whoever can bring more men to the river. When the agreement stops being fixed, the coercion does not disappear. It simply comes back, on whatever terms the stronger party finds convenient. That is what the phrase “the law of force” names. It is the default condition of the world, the thing that treaties were invented to hold back, and it is always three or four broken promises away from returning.

The Catechism says the same thing in the ordinary register of the seventh commandment: “Promises must be kept and contracts strictly observed to the extent that the commitments made in them are morally just.”^[15] The Catechism is talking about labor contracts and sales agreements when it says that. The Compendium’s whole argument is that the identical obligation runs upward into treaties, unchanged, because it is the same moral law.

A Promise Is Not A Price

Now put the Truth Social post next to that teaching and look at what it actually does. It gives two reasons for reducing the exercises. The first is cost, “with much of these costs paid for by the United States of America (as usual!).” The second is Seoul’s answer on Iran.

The cost complaint at least belongs to a recognizable moral conversation. Burden sharing among allies is a legitimate subject, and the Compendium is careful to say that nations retain real sovereignty and real freedom in what they take on; sovereignty is “an expression of the freedom that must govern relations between States.”^[16] A country may argue about who pays for what. Reasonable people have argued about it for seventy years.

The second reason belongs to a different conversation entirely. It converts an existing security commitment into a lever, and pulls the lever because a request in a separate theater, on a separate continent, was declined. Whatever else the 1953 treaty is, it is not a subscription that lapses when the subscriber declines an upsell.

Here is the Compendium again, and notice how specifically it anticipates this: relations among peoples and political communities must be “justly regulated according to the principles of reason, equity, law and negotiation, excluding recourse to violence and war, as well as to forms of discrimination, intimidation and deceit.”^[17] Intimidation is named on that list next to violence. The Church puts it there because the pressure a great power can apply to a small one usually never reaches the point of violence. It does not have to. The threat, delivered publicly, hours before an exercise begins, on a platform the whole world reads, does the work by itself.

What Happens To The Smaller Party

South Korea’s Ministry of National Defense answered on Monday that the drills would “proceed as previously notified and scheduled.” That is a careful sentence. It is also, read from Seoul, the sound of an ally who has just learned that the terms can move without warning and has decided to say as little as possible.

John XXIII saw this pattern clearly and wrote about it with a bluntness that startles me every time. Some nations, he grants, have reached “a superior degree of scientific, cultural and economic development.” Then: “But that does not entitle them to exert unjust political domination over other nations. It means that they have to make a greater contribution to the common cause of social progress.”^[18] Superiority creates duty. He goes further and denies the premise underneath every great-power calculation: “no one can be by nature superior to his fellows, since all men are equally noble in natural dignity. And consequently there are no differences at all between political communities from the point of view of natural dignity.”^[19]

He also anticipated the specific injury here. States, he wrote, have “the right to their good name and due honors.” And just as an individual may not pursue his private interests unfairly at the expense of others, “so too it would be criminal in a State to aim at improving itself by the use of methods which involve other nations in injury and unjust oppression.” He then quotes Augustine, who put the whole matter in nine words: “Take away justice, and what are kingdoms but mighty bands of robbers.”^[20]

Augustine wrote that line about Rome, and the Church has been applying it to every subsequent empire without exception, including the ones she liked.

The Iran Sentence Is The Whole Argument

Go back to the parenthesis Trump put in his own post: “While somewhat unrelated (?).” He knew. The question mark is doing the work of an admission.

The two things are unrelated in every way that matters legally. The Mutual Defense Treaty binds each party to act “to meet the common danger” from an armed attack “in the Pacific area.”^[21] It says nothing about Iran, nothing about the Strait of Hormuz, nothing about a war that began on February 28 of this year. South Korea’s president was asked for something outside the agreement, said no, and the agreement’s practical expression was reduced within days.

The Church calls this the erosion of the juridical order, and the Compendium describes what that order is supposed to be: “The international community is a juridical community founded on the sovereignty of each member State, without bonds of subordination that deny or limit its independence.”^[22] The phrase to sit with is bonds of subordination. An alliance in which the weaker party’s declining an unrelated request reduces the stronger party’s commitments has quietly become something older and simpler than an alliance of two sovereigns. One party asks, and the other had better find a way to say yes.

The Compendium’s warning about this is one line long and has the finality of a courtroom: “international law must ensure that the law of the more powerful does not prevail.”^[23]

Mutual Confidence Is A Public Good

Catholic doctrine names a practical consequence before the strategists get to it. “In order to consolidate the primacy of law,” the Compendium says, “the principle of mutual confidence is of the utmost importance.”^[24] Confidence, trust, the ordinary human expectation that a thing said will hold. The Compendium treats it as infrastructure, something a peaceful world runs on the way a city runs on water pressure.

And trust between nations is expensive to build and cheap to spend. Every ally watching Sunday’s post learned something that will sit in their planning documents for years: American commitments can be repriced in public, on short notice, over an unrelated disagreement. Japan read it. Taiwan read it. The Baltic states read it. Whether or not one exercise gets shortened by three days is almost beside the point. What moved on Sunday was the confidence, and confidence does not come back on the schedule of the news cycle.

John XXIII again, on how disputes between states are supposed to be handled when interests genuinely clash, as they sometimes will: “they must be settled in a truly human way, not by armed force nor by deceit or trickery. There must be a mutual assessment of the arguments and feelings on both sides, a mature and objective investigation of the situation, and an equitable reconciliation of opposing views.”^[25] Mutual assessment of the arguments and feelings on both sides. He put feelings in there deliberately, and a paragraph earlier explained why: “nations can be highly sensitive in matters in any way touching their dignity and honor; and with good reason.”^[26]

Where Leo XIV Has Moved The Ground

I have written about this development several times in recent weeks, and I want to keep it in its proper place rather than turning it into a refrain, but it belongs here, because this story is ultimately about war.

In Magnifica Humanitas, Pope Leo XIV teaches that war has been “revived as an instrument of international politics, while the very ethical principles that had previously limited its use are being eroded,” and states, without prejudice to the right of self-defense in the strictest sense, that the classical just war theory “which has all too often been used to justify any kind of war, is now outdated.”^[27] Leo XIV has raised the bar.

Apply his actual concern to Sunday. A war in Iran, which South Korea declined to join, is now being used as the measuring stick for what America owes South Korea in the Pacific. That is war functioning as an instrument of international politics in exactly the sense Leo names, working on a third party who is not even a belligerent. Leo XIV warns in the same encyclical about “a world in a permanent state of belligerence.”^[28] A world becomes permanently belligerent through a hundred small conversions like this one, where a relationship built for defense gets picked up and used as currency in someone else’s fight. Declarations are rarely the mechanism.

The Compendium, written twenty years earlier, reaches the same destination by a different road when it insists that tensions between political communities be resolved by common rules and negotiation, and that we “reject definitively the idea that justice can be sought through recourse to war.”^[29]

The Family Of Nations Has Members Who Cannot Leave

One more line from the Compendium, and it is the one I would put on the wall of the State Department if anyone asked me. National sovereignty is not absolute, it says, and nations can freely give up the exercise of some rights for a common goal, “in the awareness that they form a ‘family of nations’ where mutual trust, support and respect must prevail.”^[30]

Family. That word is chosen on purpose, and it carries the whole weight of the argument, because a family is precisely the association you cannot resign from when the terms get inconvenient. South Korea gave up something real in 1953. It accepted foreign troops on its soil, accepted operational arrangements no fully independent country would otherwise accept, and shaped seventy years of its national life around a promise made by a nation on the other side of the Pacific. That is what the Compendium means by freely renouncing the exercise of some rights in view of a common goal. Korea paid in advance.

Then look at the photograph again. A Korean sergeant is standing in a river, waving an armored vehicle across a bridge that Korean and American engineers built together. That bridge is what the treaty looks like when it is working. It is also what 18,000 Korean soldiers did on Monday morning while Washington argued about whether to keep showing up.

What A Catholic Does With This

You and I do not set alliance policy. So let me be specific about what this situation demands of a faithful Catholic.

It asks first for a change in how we listen. When an American president talks about a treaty as a cost, and treats an ally’s refusal as a debt, most of us hear it as ordinary politics and file it under negotiation. Catholic social doctrine asks us to hear it as a moral claim about promises and to test it as one. Ask the question the Church would ask: was something owed, and was it paid? That question is available to any Catholic reading a headline, and it produces a different judgment than the political one nearly every time.

It asks second for consistency about the moral law. We are perfectly comfortable telling a man he has to honor a contract even when it stops being profitable. John XXIII is telling us the same standard binds a government making a promise to 52 million people, and that no one attains an office that suspends it.

And it asks for prayer that is more particular than “peace in the world.” Pray for President Lee, who has to decide today how much of his country’s security he can still count on. Pray for the 28,500 Americans stationed on that peninsula, most of them very young, who will absorb whatever this becomes. Pray for the people of North Korea, who are not their government, and who have lived seventy years inside the consequences of an unfinished war.

The choice the Compendium describes is stark, and it recurs constantly: the force of law, or the law of force. There is no third option, and every generation gets asked again.

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Footnotes

1. Aaron Kidd, “Trump Calls North Korea ‘Unthreatening,’ Orders Reduction in South Korea Military Drills,” Stars and Stripes, August 16, 2026, https://www.stripes.com/theaters/asia_pacific/2026-08-16/trump-kim-jong-un-korea-military-exercises-22573400.html. ↩
2. “Trump Says US to ‘Substantially Reduce’ Military Drills with South Korea,” Al Jazeera, August 17, 2026, https://www.aljazeera.com/news/2026/8/17/trump-says-us-to-substantially-reduce-military-drills-with-south-korea. ↩
3. Yoo Jee-hye, “Trump Cites ‘Good Relationship’ with North’s Kim in Post Announcing Reduction in South–U.S. Drills,” Korea JoongAng Daily, August 17, 2026, https://www.koreajoongangdaily.com/korea/trump-cites-good-relationship-with-norths-kim-in-post-announcing-reduction-in-southus-drills/12827434. ↩
4. Rebecca Falconer, “Trump Tells Hegseth to Cut Back U.S.-South Korea Drills,” Axios, August 16, 2026, https://www.axios.com/2026/08/16/trump-us-south-korea-military-drills-cut. ↩
5. “Trump Orders Military to ‘Substantially Reduce’ Joint Exercises with South Korea,” NBC News, August 16, 2026, https://www.nbcnews.com/politics/trump-administration/trump-orders-military-substantially-reduce-joint-exercises-south-korea-rcna592832. ↩
6. “Trump Says US Will Reduce Military Exercises with South Korea, Citing Lack of Help with Iran,” CNN, August 16, 2026, https://www.cnn.com/2026/08/16/middleeast/trump-south-korea-military-exercises. ↩
7. “Trump Orders Major Cut to US-South Korea Drills as North Korea Ramps Up Missile Tests,” Fox News, August 16, 2026, https://www.foxnews.com/politics/trump-orders-major-cut-us-south-korea-drills-north-korea-ramps-up-missile-tests. ↩
8. “Trump Cites Kim Jong Un Ties in Push to Reduce South Korea Military Drills,” Newsweek, August 16, 2026, https://www.newsweek.com/trump-kim-jong-un-south-korea-military-exercises-12329549. ↩
9. Congressional Research Service, U.S.–South Korea Alliance: Background and Issues for Congress, R48877 (Washington, DC: Library of Congress, 2026), https://www.congress.gov/crs_external_products/R/PDF/R48877/R48877.7.pdf. ↩
10. John XXIII, Encyclical Letter Pacem in Terris (April 11, 1963), no. 80, https://www.vatican.va/content/john-xxiii/en/encyclicals/documents/hf_j-xxiii_enc_11041963_pacem.html. ↩
11. Pacem in Terris, no. 81. ↩
12. Pontifical Council for Justice and Peace, Compendium of the Social Doctrine of the Church (Vatican City: Libreria Editrice Vaticana, 2004), no. 436, quoting Pius XII, Christmas Radio Message (December 24, 1941). ↩
13. Compendium of the Social Doctrine of the Church, no. 437, quoting John Paul II, “Message for the 2004 World Day of Peace,” no. 5. ↩
14. Compendium of the Social Doctrine of the Church, no. 437, quoting John Paul II, “Message for the 2004 World Day of Peace,” no. 5. ↩
15. Catechism of the Catholic Church, 2nd ed. (Vatican City: Libreria Editrice Vaticana, 1997), no. 2410. ↩
16. Compendium of the Social Doctrine of the Church, no. 435. ↩
17. Compendium of the Social Doctrine of the Church, no. 433, citing Paul VI, Address to the United Nations (October 4, 1965), no. 2. ↩
18. Pacem in Terris, no. 88. ↩
19. Pacem in Terris, no. 89. ↩
20. Pacem in Terris, no. 92, quoting Augustine, De Civitate Dei, IV, 4. ↩
21. Mutual Defense Treaty Between the United States and the Republic of Korea, signed October 1, 1953, art. III, https://www.usfk.mil/portals/105/documents/sofa/h_mutual%20defense%20treaty_1953.pdf. ↩
22. Compendium of the Social Doctrine of the Church, no. 434. ↩
23. Compendium of the Social Doctrine of the Church, no. 439, quoting John Paul II, “Message for the 2004 World Day of Peace,” no. 9. ↩
24. Compendium of the Social Doctrine of the Church, no. 439. ↩
25. Pacem in Terris, no. 93. ↩
26. Pacem in Terris, no. 89. ↩
27. Leo XIV, Encyclical Letter Magnifica Humanitas (Vatican City: Libreria Editrice Vaticana, May 15, 2026), quoted in Javier Romero, “Can Wars Still Be Just? Pope Leo XIV Addresses the Issue in ‘Magnifica Humanitas,’” National Catholic Register, May 29, 2026, https://www.ncregister.com/cna/magnifica-humanitas-and-just-war. ↩
28. Leo XIV, Magnifica Humanitas, quoted in Romero, “Can Wars Still Be Just?” ↩
29. Compendium of the Social Doctrine of the Church, no. 438, citing John Paul II, Encyclical Letter Centesimus Annus (May 1, 1991), no. 23. ↩
30. Compendium of the Social Doctrine of the Church, no. 435, quoting John Paul II, Address to the Fiftieth General Assembly of the United Nations (October 5, 1995), no. 14. ↩

Books Cited

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• Catholic Church, Catechism of the Catholic Church, Second Edition, Doubleday / Image, 2003