At the start of the Cold War, American theologian Reinhold Niebuhr addressed critics of his magazine, Christianity and Crisis, who faulted him for taking a hard line against Joseph Stalin’s Russia. Niebuhr recalled that many of America’s domestic critics also believed that Nazi Germany could not be as bad as it seemed because we were not as good as we pretended. In this, he wrote, they failed to see the geopolitical realities staring them in the face.

“America is no shining light of democratic justice,” he wrote in 1947. “But that still does not change the fact that the generous nineteenth century Marxist dream of a universal classless society has changed into a nightmare of Russian tyranny, and that the free peoples of the world hope that they can count on our support in avoiding a new enslavement.”

As Vladimir Putin wages a remorseless war of aggression against Ukraine, the free peoples of the world are no doubt wondering the same thing. Indeed, in his speech to the United Nations Security Council last month, Ukrainian president Volodymyr Zelensky exposed the utter moral dysfunction of the U.N. system—an institution that was conceived, designed, and funded by the United States to ensure international peace and security: “I would like to remind you of the first article of the U.N. Charter. What is the purpose of our organization? To maintain peace. . . . Now the U.N. Charter is being violated literally from the first article. And, if so, what is the point of all the other articles?” Zelensky pressed home the point: “We are dealing with a state that turns the right of veto in the U.N. Security Council into a right to kill.” As he spoke, fresh evidence of Russian atrocities against civilians was being uncovered in Bucha and other cities in Ukraine.

In confronting the challenge that Russia now poses to international security, it’s vital to consider the role that America played in establishing a new world order at the end of the Second World War: a burden of leadership unprecedented in modern diplomatic history.

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At its best moments, the United States has rejected both isolationism and utopianism and adopted a policy of realism—not a manipulative Machiavellian realism, but something that Niebuhr called “Christian realism.” It is a political outlook that takes seriously the biblical concept of the Fall of man, while avoiding cynicism about mankind’s inherent dignity and capacity for self-government. As Niebuhr viewed it, Christian realism draws upon America’s political and religious ideals—American exceptionalism—to help constrain its immense military and economic power and to deploy this power in the cause of human freedom.

Toward this end, for example, the United States led an alliance of democratic nations that agreed to fight the Axis Powers until final victory. On January 2, 1942, representatives from 26 countries—which Franklin Roosevelt called the “United Nations”—issued a declaration of war aims. They explained that victory was essential in order “to defend life, liberty, independence and religious freedom and to preserve human rights and justice” in the lands of the signatory nations “as well as in other lands.”

The core doctrine of the U.N. Charter protecting national sovereignty, “based on respect for the principle of equal rights and self-determination of peoples,” owes a massive debt to American constitutionalism and the principle of government by consent. Likewise, the Universal Declaration of Human Rights, drafted in the wake of Nazi atrocities, draws inspiration from the U.S. Bill of Rights. Indeed, the UDHR’s affirmation of mans’ natural and unalienable rights echoes the natural-rights arguments in John Locke’s Second Treatise of Government, a favorite among the Founders: “All human beings are born free and equal in dignity and rights. They are endowed with reason and conscience and should act towards one another in a spirit of brotherhood.”

Here is the imprint of American idealism on the political architecture of the United Nations. Charles Malik, the Lebanese ambassador to the United Nations and one of the drafters of the UDHR, confessed his admiration for America’s democratic principles: “I cannot imagine the declaration coming to birth under the aegis of any other culture emerging dominant after the Second World War.”

Nevertheless, idealism requires the ballast of Christian realism. This brand of realism was missing when the permanent membership of the U.N. Security Council included the Soviet Union—the epicenter of atheistic communism, a collaborator with Nazi Germany in the dismemberment of Poland, and a ruthless dictatorship without regard for basic human rights. This Faustian bargain guaranteed that an institution at the heart of the U.N. system would be fatally compromised.

Indeed, the United Nations, for all of the good intentions of its founders, was a project crippled by liberal delusions about human nature and the nature of political societies. “In this liberalism there is little understanding of the depth to which human malevolence may sink and the heights to which malignant power may rise,” Niebuhr wrote in Christianity and Power Politics. “Some easy and vapid escape is sought from the terrors and woes of a tragic era.”

The international crisis set off by Russia’s invasion of Ukraine has revealed the abject failure of escapism as a substitute for political realism. “Are you ready for the dissolving of the U.N.?” asked Zelensky. “Do you think that the time of international law has passed?” He bluntly challenged America and her democratic allies to help Ukraine check Russian aggression and expel Russia from the Security Council—or dissolve the institution outright.

There is at this hour a critical need for the United States to think and act creatively, with sober moral judgment, as it exercises its leadership responsibilities in light of a resurgent Russia. It has done so in the past—to great effect.

Within months of the end of the Second World War, for example, America acted decisively to hold the Nazi leaders to account for their wartime crimes. Alone among the great powers, the United States insisted upon an international tribunal, the Nuremberg trials, to judge the atrocities committed by the Nazi regime. America rejected the call for mass executions or show trials.

Instead, it set a new standard of justice for punishing crimes against humanity—not unlike the crimes now being committed by Russian forces in Ukraine. Robert Jackson, the lead prosecutor for the United States at the Nuremberg trials, put the case thus in his opening statement: “The wrongs which we seek to condemn and punish have been so calculated, so malignant, and so devastating, that civilization cannot tolerate their being ignored, because it cannot survive their being repeated.” The Nuremberg trials are widely credited with helping Germany to confront its Nazi past and reintegrate itself into the democratic West.

When Joseph Stalin launched a Soviet blockade of democratic West Berlin to force the withdrawal of American troops from West Germany, the United States rejected both isolationism and militarism. President Harry Truman ordered American pilots into the city—not on bombing raids, but on a mission of rescue. Over the next 323 days, the Berlin airlift delivered 2.3 million tons of food and fuel to preserve the lives and freedoms of their former enemies. Stalin ended the blockade, and West Berlin remained free and independent.

When the Soviet Union threatened to extend its grip over the nations of Western Europe and reduce their populations to servitude—as it had done in Eastern Europe—the United States stepped into the breach.

General George Marshall, who witnessed firsthand the ravaging effects of war on civilian populations, conceived of an economic lifeline for Europe. Begun in 1948, the Marshall Plan, costing U.S. taxpayers more than $13 billion (about $135 billion in today’s dollars), stabilized the vulnerable economies of 16 nations. Soft power was backed by hard power: the creation of the North Atlantic Treaty Alliance, the most successful political–military alliance in history. These policies rescued Western Europe from social breakdown and Soviet rule and made possible the astonishing transformation of illiberal societies into peaceful, free-market, democratic states.

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America’s Cold War policy was rooted in its civilizational confidence: the belief that the American creed of human freedom and equality, based upon mankind’s unalienable rights, applied to people everywhere. In other words, American exceptionalism carried implications for everyone striving for a more just and humane world.

At the end of the Second World War, the United States was correct to insist that international peace and security depended upon the protection of man’s basic rights and freedoms. In the words of the U.N. Charter, each member state must “reaffirm faith . . . in the dignity and worth of the human person” and “in the equal rights of men and women and of nations large and small.” The rejection of this concept leads only in one direction: It invites the forces of disorder, violence, and dictatorship, which thrive on democratic weakness.

Even as the United States and Great Britain were battling Nazi Germany during the Second World War, Winston Churchill worried about Russian imperialism: “It would be a measureless disaster if Russian barbarism overlaid the culture and independence of the ancient States of Europe.”

The shadow of Russian barbarism has returned—and the impulse toward isolationism will not drive it out. As Reinhold Niebuhr warned, the exercise of American power always involves a measure of risk and hubris, but “the disavowal of the responsibilities of power can involve an individual or nation in even more grievous guilt.”