At a baffling moment full of Russian intrigue, made-for-reality-TV summitry, presidential Twitter rants, and trade wars, history can offer perspective, if not comfort. The ancient Greeks often understood our world more clearly than we do. Thucydides’ history of the Peloponnesian Wars between Athens and Sparta, many modern scholars now recognize, was intended as a work of Greek tragedy. It provides a morality play for the ages, offering insights into the foreign-policy challenges facing the United States in the years ahead, even after Donald Trump’s presidency.

Athens, the protagonist, is a state like the United States founded on virtuous principles. As its wealth and power grow, however, it seeks to extend its influence beyond its borders. Then, at the height of that power, following the rule of Pericles, not only does Athens begin to lose its democratic character, but it so outstrips others in its military might that it no longer feels bound by the moral values and sense of community that held the ancient Greek world together.

As in any Greek tragedy, Athens eventually falls prey to moral hubris and overreaches. In one of Thucydides’ more memorable examples, its navy surrounds the small island of Melos and demands its allegiance. The outnumbered Melians famously protest that when it comes to matters of war and peace, “the strong do what they can; the weak what they must.”

For generations of students of foreign policy, the line has been used to demonstrate how circumscribed moral choice is in an anarchical world. However, Thucydides perhaps wants us to understand as well that for the stronger power “can” differs from “must” in that it does afford some room for moral judgment.

The Athenians, though, prove deaf to the Melians’ pleas for mercy. When the Melians ultimately surrender, the Athenians are unsparing in victory and slaughter all the male inhabitants, while selling the women and children into slavery. After a number of other acts of barbarity, the Athenians not only lose their moral standing and leadership of the ancient Greek world, but eventually the war.

It is a fitting parable for our age. The United States risks the tragedy which befell Athens becoming its own—and not simply because of the excesses of its current president. America lost its way with regard to foreign policy well before Donald Trump became president, and it is far from clear the United States will simply reassume its global leadership position after he departs.

The End of Unipolarity

What will U.S. foreign policy look like after Trump? Looking beyond the daily chaos he sows, one thing is clear: America’s unipolar moment—its nearly three decades following the Soviet Union’s collapse as the world’s sole superpower—has ended. No other country can yet match the United States in terms of military, economic, or political power, but the United States no longer possesses the ability to shape world events as it did in the Cold War’s aftermath.

Moreover, in retrospect, this unusual period of unchallenged American power may have been as much a curse as a blessing for the United States. With the fall of the Berlin wall in 1989, and then the Soviet Union’s slow implosion over the succeeding two years, the United States lost the lodestar which long guided its foreign policy: the need to counter communist expansion.

With the Soviet Union’s demise, America found itself the unrivaled and lone superpower on earth. But it lost at the same time the moral clarity that a mortal enemy provides. The domestic consensus undergirding U.S. foreign policy slowly evaporated as well, and the very tenor of that policy, in the absence of a compass to steer it, began to change.

The United States has lacked a coherent national-security strategy since.

The Search for a Post–Cold War Strategy

Successive U.S. administrations lurched from one policy to another as they grappled with the challenges of a post–Cold War world. George H. W. Bush struggled to define a new balance of power in Europe to address the vacuum left by the collapse of the Eastern bloc. While reunifying Germany and bringing it solidly into the western camp, his administration sought to mollify the Russians with promises that NATO would not expand eastward.

Bill Clinton, amidst a popular wave of “end of history” triumphalism, proceeded to enlarge NATO to include East European members and to attempt to spread many of the benefits of the liberal order across the globe. At the same time, he wrestled—in places such as Somalia, Rwanda and Bosnia—with the question of how universal America’s responsibility was to police that order.

The 9/11 attacks placed the United States momentarily on the defensive, forced to undertake extensive measures to protect the homeland. But George W. Bush quickly pivoted to the offense, using the attacks as a causus belli to invade Afghanistan and Iraq in a misguided attempt to eradicate terrorism and remake the Middle East in America’s image. Some of the president’s closest advisors championed the idea of a new American imperialism to impose order on an increasingly volatile world.

Barack Obama sought to course correct, endeavoring to shrink America’s military footprint in the Middle East while offering “a new way forward” to the Muslim world and, to Iran, to “extend a hand if you are willing to unclench your fist.” At the same time, he sought to “pivot” America’s resources and attention towards Asia. But with the Arab Spring, his commitment to the kind of positive change being called for by citizens in the streets collided with his reticence to devote additional U.S. resources to, or offend long-standing partners in, the region.

These repeated U-turns in U.S. foreign policy, which are sufficient to give any ally whiplash and to throw into question American intentions and commitment, did not start with Donald Trump. Without the competition provided by another superpower or the need to work with allies, America gradually lost its focus and its way in the world. Freed of these constraints, prudence—that prized ability in diplomacy to match ends to means—went out the window. Time and again, the United States began to ignore international law when it suited its interests, to turn a deaf ear to the moral arguments of the rest of the international community, and to renege upon its global responsibilities.

The bipartisanship that long characterized U.S. foreign policy during the Cold War frayed. Many liberals succumbed to the illusion that America could resolve every violent conflict, every human-rights abuse, and every violation of democratic norms that occurred around the globe; many conservatives to the fallacy that neither international institutions nor allies could be trusted and America was best served acting alone in the world.

Trump Goes to Washington

Flash forward to the present. In May, in a scene worthy of The Apprentice, President Donald Trump announced to the world that the United States was quitting the Iranian nuclear deal. With great ceremony more appropriate to the signing of the Louisiana Purchase, he then put his signature, with an exaggerated flourish, to a two-page presidential memo resuming sanctions. Not because Iran was violating the terms of the deal. Not because he had a better alternative to offer. But simply because he could. A month later, he was trying to forge a very similar deal with North Korea.

Welcome to America’s Melian moment. President Trump seems intent on demolishing an international order that for seventy years has provided the United States and the world unprecedented stability and prosperity. As his repudiation of the Iran nuclear deal made clear, he appears determined to cast aside entirely America’s international responsibilities to pursue instead whatever advances a very narrow definition of its self-interest—the rest of the world be damned. He has signaled an interest in pulling back U.S. troops from the Middle East, Europe, Japan and the Korean Peninsula. He is holding longstanding international institutions such as the G-7, NATO, the WTO, and NAFTA hostage, threatening that if the United States does not receive a greater share of the benefits, it will abandon these institutions entirely.

Donald Trump’s foreign policy may be a fitting conclusion to America’s unipolar moment and the unraveling of its domestic consensus as to what U.S. values, interests, and policies should be in a rapidly changing world. His bizarre and bellicose approach to the rest of the world is extreme to the core, but not an unsurprising consequence of an American foreign policy that has been adrift since the Soviet Union’s collapse.

The irony is that an avowedly conservative president, backed by one of the most conservative Congresses in history, is now the one untethering the United States altogether from the rules of the international order. For true Burkean conservatives, this is the ultimate nightmare: an unpredictable superpower careening from crisis to crisis without strategy or constraints. “But what is liberty without wisdom and without virtue?” Edmund Burke wrote. “It is the greatest of all possible evils; for it is folly, vice, and madness, without tuition or restraint.” The president’s nationalistic rhetoric, his public spats with longstanding allies, and his puzzling admiration for authoritarian strongmen are full of folly, vice, and madness.