Opinion | Donald Trump’s Threat to the Global World Order

The global legal order rests on a kind of collective act of faith. For it to work, nations must trust that other nations will behave as if its principles matter. The system is not so unlike the dollar in this respect: It holds value only when — and only because — most of those who use it believe that it does.

This is why Donald Trump’s re-election to the American presidency is such a threat to global peace and security. He is — as an elected official and as a person — committed to breaking principles, not maintaining them. He understands and appreciates the value of the dollar. The global legal order? Not so much.

The last time he was president, Mr. Trump withdrew from critical treaties, launched what critics have deemed unlawful military strikes in Syria and on the Iranian general Qassim Suleimani in Iraq, and set off a damaging trade war with China. This time, his incoming administration appears poised to do far worse. His choice for national security adviser, Representative Michael Waltz, introduced legislation last year to use military force against drug cartels in Mexico. His pick for defense secretary, Pete Hegseth, has championed service members accused or convicted of war crimes. His choice for director of national intelligence, Tulsi Gabbard, is an apologist for both the Syrian dictator Bashar al-Assad, who has massacred his own people, and Russia’s president, Vladimir Putin, who started an illegal war on Ukraine and is under an arrest warrant from the International Criminal Court.

Together with Mr. Trump’s, their ideas embody the rejection of a system that is grounded in the idealistic — but until now remarkably successful — faith in the willingness of nations to abide by a set of shared principles that guide their behavior. If they have their way and America’s commitment to supporting this legal order ceases, we may find out how much the global rules — and principled American leadership in support of them — really matter.

For 80 years, chief among these principles has been the prohibition on war, and, with it, territorial conquest. This was not always a given. For much of modern history, nations operated in a system in which “might makes right.” It was in the years after World War I that nations first renounced the resort to war “as an instrument of national policy.” In 1945, with Germany and Italy having surrendered and Japan on the brink of defeat, 50 nations gathered in San Francisco to sign the United Nations Charter, which declared that “all members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state.” This commitment has been remarkably effective: Wars of aggression and territorial conquest, once common, have become exceedingly rare.

This transformation created the foundation for a new global order. It gave rise to a host of new international organizations — the United Nations, the World Bank and the World Trade Organization, to name a few. And it set the stage for thousands of international agreements, from the 1949 Geneva Conventions to the 1970 Treaty on the Non-Proliferation of Nuclear Weapons to the 2016 Paris Agreement on Climate Change. With nations largely free of fear that trading partners would attempt to seize the gains from trade by force, global trade has flourished. Peaceful cooperation among countries is at a high — on everything from human rights to freedom of the seas to exploration of outer space to public health.

Not every country has to believe in the basic principles that underpin the global legal order for them to be effective. All that is necessary is for enough to be both committed to the principles and willing to penalize norm-breaking behavior. Indeed, nations don’t even have to know that they are following international law for it to shape their behavior. They just need to know that if they take certain actions — say, invading their neighbor — there will be hell to pay.

Over the past eight decades, the United States has played a key role in helping to maintain the system. When Iraq invaded Kuwait, Washington rallied the world to come to Kuwait’s defense. The United States has supported the system through nonforceful measures as well, pioneering an extensive system of economic sanctions to harness the power of the dollar to bring down the hammer on nations that run afoul of the rules. And it has used moral suasion to try to bring other nations along. Washington was critical in building a coalition to respond to Russia’s unlawful invasion of Ukraine in 2022. Though the United States has violated international law, no other nation has demonstrated the power, when it wishes, to marshal the world to act in support of an abstract principle.

Now all of that may be in jeopardy. Mr. Trump has said that he will end the war in Ukraine by Inauguration Day, something that could be done only by forcing Ukraine to accept Russia’s unlawful seizure of some 20 percent of its territory. This would not only allow Mr. Putin to get away with and profit from his crime of aggression, it would also send a signal to leaders the world over: the United States is no longer going to back the global order. Equally worrisome is Mr. Trump’s decision to fill his cabinet with China and Iran hawks, enthusiasts for covert action, and others itching to use U.S. military force as an all-purpose tool, raising the question whether the United States might use unlawful force abroad itself.

Some will say that the legal order that followed World War II was a mirage all along — that it was never what we believed or hoped it was. And there is certainly some truth in that. Since 2001, the United States has waged a global war against terrorist groups throughout the Middle East, stretching and sometimes breaking international legal limits on the use of force. Much of the world believes the United States’ 2003 war in Iraq was just as unlawful as Russia’s war in Ukraine is today. China, too, has been quietly gobbling up islands, reefs and “rocks” in the South China Sea to which it has no lawful claim. And violations of international humanitarian law have been rife, including in Ukraine, Sudan and Gaza.

And yet, for all its obvious shortcomings, the global order of nearly eight decades has been one of unprecedented stability. Claims that the rules that have shaped the international landscape since the Second World War are irrelevant or obsolete are shortsighted: The world was far more violent and far less prosperous when states could use force free of modern constraints.

There are many in Washington and across the country who believe that returning to a world in which might makes right is in America’s best interests. After all, the United States undoubtedly has the most powerful military in the world. Why not use it? But, as we have repeatedly learned, military power has its limits. More than two decades of counterterrorism operations in the Middle East ought to have taught us that. In the long term, a system grounded in force rather than principle is far more costly to maintain — and far less effective.

Indeed, this is another respect in which the international legal order is like the dollar: It is a store of value. The system’s rules carry immense power, because as long as everyone shares the collective belief that the rules matter, they do, in fact, matter. This is why the United States’ capacity to shape the international legal order in the postwar era has been a source of unmatched global influence. As soon as nations lose faith, however, the system will quickly crumble — and America’s influence with it.

It is possible that Republican members of the Senate will recognize that it is shortsighted to torpedo the international order that the United States helped build. And some members of the U.S. military might try to restrain Mr. Trump’s most dangerous impulses. But truth be told, the political and legal constraints on the president are modest, thanks to a decades-long bipartisan effort to strip away nearly all constraints on the president’s powers to determine U.S. foreign policy. The president now has an almost entirely unfettered capacity to order the use of military force, thanks to the erosion of constitutional constraints and the gutting of the 1973 War Powers Resolution, a law meant to limit the president’s ability to wage war unilaterally. Congress has not authorized the use of military force since 2002, and vanishingly few of those currently serving in Congress have ever voted to authorize its use. Yet the United States has an active military presence in over a dozen countries.

There is some reason for hope. The global legal order has depended heavily on the United States to manage and maintain the system. There are also 192 other states in the United Nations. If America no longer was willing to act to maintain the postwar consensus, it would be up to these states to decide how to respond. Would they let it collapse? Or would they try to do more to hold it together?

While no other nation on its own wields the same power as the United States, together they can do far more than one country ever could. The international system empowers every nation to act independently: to enforce the rules, or to ignore them. The future of the global order — and everything it has delivered to the world — depends on what they decide.

Oona A. Hathaway is a professor of law and political science at Yale University and a nonresident scholar at the Carnegie Endowment for Peace.

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