“War,” the Prussian military thinker Carl von Clausewitz wrote, “is a mere continuation of policy by other means.” If there is one line that virtually every Army officer learns from Clausewitz’s posthumously published 1832 book, “On War,” it’s that description of the purpose of armed conflict.
Those words were among the first that popped into my head when I woke up Saturday morning to the news that the American military had attacked Venezuela, seized its dictator, Nicolás Maduro, and brought him to the United States to face criminal charges.
The reason those words occurred to me was simple — the attack on Venezuela harks back to a different time, before the 19th century world order unraveled, before two catastrophic world wars, and before the creation of international legal and diplomatic structures designed to stop nations from doing exactly what the United States just did.
One of the most important questions any nation must decide is when — and how — to wage war. It’s a mistake, incidentally, to view General Clausewitz as an amoral warmonger. He wasn’t inventing the notion he describes; he was describing the world as it has been. His statement is a pithy explanation of how sovereign states viewed warfare for much of human history.
When a strong state operates under the principle that war is just another extension of policy, it is tempted to operate a bit like a mob boss. Every interaction with a weaker nation is tinged in some way with the threat of force — nice little country you have there. Shame if something happened to it.
This is not fanciful. In a telephone conversation with The Atlantic’s Michael Scherer, President Trump threatened Venezuela’s new leader, Delcy Rodríguez, who served as Maduro’s vice president. “If she doesn’t do what’s right,” Trump said, “she is going to pay a very big price, probably bigger than Maduro.”
Diplomacy and economic pressure are almost always still a first resort for powerful nations, but if they fail to achieve the intended results — well, you can watch footage from the American strike in Venezuela to know what can happen next.
But the Clausewitzian view isn’t the only option for nations and their leaders. There is a better model for international affairs, one that acknowledges the existence of evil and the reality of national interests, but also draws lines designed to preserve peace and human life.
Carl von Clausewitz, meet Thomas Aquinas.
In Summa Theologica, written in the 13th century, Aquinas outlined three cardinal requirements of what came to be known as just war theory.
First, war must be waged through the lawful operation of a sovereign and not through the private adventurism of ambitious individuals.
Second, the war must be based on a just cause. National self-defense or collective self-defense are obviously just, for example.
Third, there must be a just purpose, namely the advancement of good and the avoidance of evil.
One way to think about the shifting patterns of warfare is that humanity seesaws between Clausewitz and Aquinas. Strong nations impose their will on the weak and then — eventually — try to impose their will on each other. When catastrophe results, as it invariably does, they turn back to Aquinas.
You can actually see the results of this shifting approach across the sweep of history. An analysis of global deaths in conflict shows that war is always with us, but its intensity waxes and wanes. Periods of extreme suffering and death are followed by periods of relative quiet, followed again by an age of horror.
Consider history since World War I. After the ongoing slaughter of trench warfare, the world attempted to ban aggressive warfare and to establish an international institution — the League of Nations — to keep the peace.
The League failed, in part because the United States refused to join, and after an even more horrible world war, the world tried again, this time under American leadership.
Echoes of Aquinas are all over the U.N. Charter. Article 2 of the United Nations Charter bans aggressive warfare (taking away a key tool in the Clausewitz toolbox); Article 51 permits individual and collective self-defense to keep great powers in check; and Chapter V established a body (the Security Council) that’s designed to keep the peace.
No one would argue that the system is perfect. We’ve seen wars of aggression since World War II, but the system has achieved its primary goal. The world has been spared total war.
The Aquinas model, however, has to fight two foes — the will to power and the loss of memory. Just war theory demands restraint from the powerful. It asks great powers to forgo imposing their will — even to the point of subordinating their short-term national interests to the long-term aspiration of international peace and justice.
That’s where our loss of memory comes into play. Restraint is more persuasive when people actually remember a world war, and the people who built the United Nations and NATO had been through two. In that sense, the moral argument against aggressive war has practical application.
The world has seen what happens when the will to power dominates world affairs, and its leaders know (or should know) that the most catastrophic conflicts can start from the most modest beginnings.
When Gavrilo Princip took aim at the Archduke Franz Ferdinand in Sarajevo in 1914, for example, and Austria-Hungary mobilized against tiny Serbia, how many world leaders grasped that more than 16 million people would die in the war to come?
When memory fades, the Clausewitz model grows more tempting — in part because it can achieve quick results, just as it did in Venezuela early Saturday morning.
Not even the angriest opponents of Trump’s intervention in Venezuela should whitewash the rule of Maduro. He was a corrupt and violent dictator who impoverished and oppressed his people.
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The economic numbers tell one version of that story. In 2012, the year before Maduro took power, the gross domestic product of Venezuela was more than $372 billion. In 2024, it was just under $120 billion — a terrible collapse.
He retained power only by defying democracy. In 2024, election observers believe he lost his bid for a third term by a more than 30-point margin. His opponent, Edmundo González, won more than 65 percent of the vote, and Maduro won just over 30 percent. The official tallies, however, gave Maduro the victory.
But talking about G.D.P. numbers and vote totals seems inadequate when addressing the pure human misery caused by the Maduro regime. Since 2014, almost 8 million Venezuelans have fled the country to escape poverty, corruption and oppression. This represents more than a quarter of Venezuela’s population before Maduro was president.
Even so, the ends do not justify the means.
The Trump administration — acting entirely on its own and without seeking congressional approval — decided it was in the best interests of the United States to remove Maduro from power.
But when it struck, it violated every principle of just war.
First, Trump acted unilaterally, turning his back on the sovereign constitutional requirements of American law. He did not consult with Congress. He did not secure a declaration of war. He simply attacked a sovereign country on his authority alone.
Marco Rubio, the secretary of state, has argued that the administration’s action wasn’t an act of war, but rather a “law enforcement operation” and that the Defense Department merely protected the arresting officers.
This defense is laughable. Under that reasoning, a president could transform virtually any war into a law enforcement operation by indicting opposing leaders and claiming that the large military forces needed to secure the leader’s arrest were simply protecting law enforcement. That’s not an argument; it’s an excuse.
Second, Trump struck without a casus belli, without just cause recognized by international law and the U.N. Charter. As Jack Goldsmith, a law professor at Harvard and a former assistant attorney general for the office of legal counsel under President George W. Bush argued in a post on his Substack, the attack “pretty clearly violates the charter,” even if there is no clear way to enforce the charter’s commands.
Third, while removing a dictator from power can be a just end, Trump’s decision to turn his back on the democratically elected opposition is profoundly troubling. That the remaining elements of a corrupt regime still govern the country — subject to American demands to negotiate oil deals with American companies — risks perpetuating corruption and oppression at the expense of freedom and democracy.
Nothing here is new. In a sharp piece for The Free Press, the historian Niall Ferguson argued that Trump’s attack on Venezuela was a piece of a much larger whole, the restoration of the politics and diplomacy of 1900 — the years before the catastrophe of the First World War.
The gunboat diplomacy of the Gilded Age certainly meant that the United States dominated Central and South America. It imposed a quasi-colonial reality on the region. Each nation developed under at least some degree of American oversight. Every nation was only as sovereign as the United States allowed it to be.
Trump’s attack on Venezuela didn’t take place in a vacuum, either. In December, the administration released its National Security Strategy paper that put the Western Hemisphere first.
The document addressed the Americas before it addressed Asia, Europe and the Middle East, and it declared that the United States will “reassert and enforce the Monroe Doctrine to restore American pre-eminence in the Western Hemisphere.”
The president already has a name for his revival of 19th Century American foreign policy: the Donroe Doctrine.
At the same time, the paper created a dangerous distance between the United States and its European allies. It declares that Europe must “stand on its own feet and operate as a group of aligned sovereign nations, including by taking primary responsibility for its own defense.”
In isolation, that statement isn’t terribly problematic. The nations of Europe are rich enough and strong enough to shoulder most of the burden of collective defense. American allies, though, contribute more than many Americans may think. According to a recent RAND study, America contributed roughly 39 percent of the total defense burden by 2023 — a number that has dropped substantially since the end of the Cold War.
Trump has embraced the Donroe Doctrine enthusiastically. He’s engaged in economic warfare against Canada and Mexico. He’s said that Canada should be America’s 51st state. He has designs on Greenland, part of the sovereign territory of Denmark, a NATO ally.
That brings us back to the fatal flaw of running the world through spheres of influence and the amoral approach to war as an extension of policy. Smaller nations don’t want to be dominated by the strong, and strong nations don’t want to see their rivals get stronger. So they make alliances. In 1914, Serbia had Russia, and Belgium had Britain. In 1939, Poland had France and Britain.
That’s exactly how regional conflict turned into global war.
If Americans wonder why any South American regime would seek closer ties with other foreign powers, perhaps we should ask what their history has been with the United States and what the people of South America think about an aggressive revival of the Monroe Doctrine.
There are better and worse ways to argue about Trump’s approach.
The worse argument is to say that Trump set a precedent with his intervention in Venezuela — a precedent that nations such as Russia, China and Iran will be eager to follow in their own respective spheres of influence, and we will have no standing to object when our adversaries take the same approach to countries in their spheres of influence that we took in ours.
But Vladimir Putin’s Russia, Xi Jinping’s China and revolutionary Iran have never had the slightest concern for just war theory or any moral argument. They’re held in check (to the extent they are) by deterrence, or, when deterrence fails, raw military force.
The better argument recognizes that there will never be a unanimous embrace of just war theory. It recognizes that the U.N. Charter is doomed to often be more aspirational than operational.
This argument recognizes that the world order doesn’t depend on every great power for its existence, but it does depend on the greatest power — the United States. Put another way, our national commitment to Aquinas keeps Clausewitz at bay.
We can barely keep the world order together when only three of the five permanent members of the Security Council — the United States, Britain and France — comply with the U.N. Charter and international law. But if the United States joins Russia and China in their approach to armed conflict and international relations, then the Western postwar consensus is truly dead.
America First isn’t necessarily isolationist — there’s nothing isolationist about arresting the leader of a sovereign nation and pledging to “run” it, but it is myopic.
It pursues the sugar high of national power at the expense of justice and peace. You can see that Trump is on that sugar high right now. On Sunday night, NBC’s Sahil Kapur reported that Trump was still saying, “We’re gonna run” Venezuela. “If they don’t behave,” Trump added, “we’ll do a second strike.”
But Trump wasn’t just thinking about Venezuela. “Colombia is very sick, too,” he said. Cuba is “ready to fall.” He also threatened to strike Iran if Iran kills protesters and brought up Greenland again: “We need Greenland from the standpoint of national security.”
If there is anything that could decisively wreck NATO, it would be an attempt to annex Greenland. Annexation could conceivably empower Denmark to invoke Article 5, the collective self-defense provision of the North Atlantic treaty, against the United States.
But there’s a further problem: The true international norm is that when the strong dominate the weak, the weak try to become strong.
That can mean alliances with enemies. That can mean global rearmament. That can mean nuclear proliferation. It can also mean that a foolish world once again endures the high cost of forgetting what it’s like when great powers go to war.
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