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.

An untethered America, the creator of the liberal international order, now presents its greatest threat.

The Art of Diplomacy

American leaders such as Franklin Roosevelt and Harry Truman, Gen. George C. Marshall and Dean Acheson, Sens. Arthur Vandenberg and J. William Fulbright, were indispensable in shaping today’s international order. From the wreckage of World War II, they forged a community of states governed increasingly by laws and institutions rather than dictated by power.

They did so less by flexing America’s massive military might than by playing the role of the peacemaker. Like the best teachers on a crowded school playground, American leaders helped diffuse conflicts before they occurred, broke up the fights when they did, and tried to find enduring solutions to bridge differences—especially when it came to events in Europe.

Whether in the immediate aftermath of World War II, at the height of the Cold War, during the collapse of the Soviet Union, or in the midst of the wars in the Balkans, America’s finest statesmen worked to envision what positive change could look like, then, mustering all elements of its national power and that of its allies, exercised leadership in order to realize that vision. Pax Americana was notable because the United States largely eschewed the methods employed by the imperial powers of the past. At its best, America did not attempt to impose its will by force on other countries, nor to divide and rule. Instead, it sought to build institutions that promoted cooperation while mitigating conflict. Other countries consented to participate because they recognized the benefits that would accrue to them and the world more generally.

President Trump has demonstrated time and again that he is not that kind of leader. Diplomacy requires patience, focus, finesse, the building of relationships and trust, long-term vision, and strategy—traits that are not his strengths. He appears to have built his real estate fortune by outmaneuvering competitors, strong-arming regulators, suing critics, sometimes stiffing suppliers, and often borrowing recklessly. He seems determined to conduct America’s foreign policy in the same fashion, preferring to be the bully on the playground to the peacemaker. But his America First policies risk killing the goose that keeps laying the golden eggs, in a vain effort to get one additional egg for ourselves.

As Athens demonstrated in Melos, bullying should not be confused for a foreign policy. American greatness has come not from doing great deals at the expense of others, but erecting lasting institutions that advance stability and prosperity for all. Winston Churchill once said, “To build may have to be the slow and laborious task of years. To destroy can be the thoughtless act of a single day.” When the United States defines its national interests in very narrow, zero-sum terms, it risks not only the collapse of the international order that it and its allies spent seventy years laboriously building, but also surrendering any claim to global leadership.

Picking Up the Pieces

What kind of world will remain after Trump’s presidency? The next American president, whether Democrat or Republican, will inherit a nation and a world in disarray. America’s fate need not be that of Athens’, though, provided it can summon the liberal internationalist spirit of its post–World War II diplomacy and recalibrate it with a dose of conservative realism for a new era in which America is no longer the dominant power. With its unipolar moment behind it, America’s foreign-policy choices will be more constrained, but as Thucydides inferred, it will still have choices.

The next American president’s challenge will be a quite difficult and fundamentally conservative one: to restore at home the integrity of American democracy and the constitutional restraints that are integral to its proper functioning, and to restore abroad America’s credibility as a nation and the trust of its friends and allies. This will not be a time for ambitious ventures abroad but for shoring up the American political system and its most critical foreign alliances. The next president will have to spend significant time explaining to a tired and highly skeptical American public why the United States needs to remain engaged internationally and reaffirming to other nations its readiness to live within the rules of the international system and to harness its power to achieve common ends.

The world that the next American president will inherit will be a multipolar one. While the United States will continue to possess overwhelming military superiority—it outspends annually the next seven military powers combined on defense—other poles of power have emerged that will matter going forward, from economic to political to diplomatic to cultural. China, Russia, and Europe will be important players on the global stage, while Brazil, India, Saudi Arabia, Iran, South Africa, and possibly Nigeria will play pivotal roles in their particular region, if not also globally.

The world also will be far more tumultuous. In the absence of U.S. leadership, regional powers with far more narrow-minded agendas are already stepping forward to fill the vacuum: Russia in parts of Eastern Europe; Iran, Saudi Arabia, and Russia in the Middle East; and China in Asia. Meanwhile, many weak states, lacking the capability to deliver even the most basic services to their citizens or to compete successfully in the global economy, risk collapsing into civil war. As we have already witnessed in places such as Syria, the spillover effects for neighboring countries can be catastrophic, in terms of mounting insecurity, refugee flows, economic dislocation, and armed violence by non-state actors. Absent international leadership to help maintain stability, the chaos will only spread.

We can only hope that the growing tumult will remind thoughtful Americans—Republicans and Democrats alike—of the importance of international leadership, international alliances, international law, and international institutions. Hopefully, it will help shake off the comfortable illusion that the peace and prosperity enjoyed over the past seventy years will continue, simply because it has endured for so long. Just as democracy must be tended and defended if it is to survive, so too must international order. While the state system will always be anarchical— without an overarching authority to enforce order—it need not be chaotic.

President Trump’s most enduring contribution to America’s foreign-policy debate may be to underscore that the United States can no longer exercise global leadership alone. Not only does America no longer possess the resources, but as the 2016 elections made clear, large sections of the electorate no longer have an interest in supporting an open-ended commitment of U.S. lives and treasure across the globe for that purpose.

This does not mean that U.S. leadership is not needed in the world—if anything, it is more essential than ever. The United States may remain the indispensable nation—with its leadership key to global stability—but it can no longer provide that stability without powerful partners.

In concert with the other major powers, the next American president will have to rethink and reconfigure existing international institutions to meet the challenges of a changed world. He or she will have to engage in wide-ranging discussions with allies and adversaries alike about the nature of the global challenges we face, where we have shared interests in addressing them, and what international institutions could best enable us to work together to do so.

The next American president should seek to rejuvenate the international system on the basis of a two-tiered architecture: With China, Europe and Russia, he or she should seek agreement on the basic norms of the international system for the twenty-first century—from the sovereign rights and obligations of states, to the rules of modern warfare, to the terms of global trade, to the safeguarding of a warming planet. (What are the minimal rules that will permit us to coexist together?) Simultaneously, with our democratic allies in Europe and beyond, he or she should seek to deepen our existing cooperation on a far broader range of issues where we find common ground, including defending democracy, promoting deeper economic integration, advancing basic human rights, and investing in the clean energy technologies that will power the future. (How can like-minded democracies work together to improve the state of the globe over time?)

Above all, the next American president will need a national-security strategy. A strategy supported by Republican and Democratic leaders alike, and one which matches ends to means. Prudence will be key to getting America back on track and avoiding the fate that befell Athens. The American people must understand that there are real limits to U.S. power, but that through careful diplomacy, the country can help reshape the international order in ways that bend history in the general direction of open markets, individual freedom, and relative peace.

Only through a sober understanding of both its objectives and the limits of its capabilities can the United States continue to provide leadership to the world, even as that world becomes increasingly multipolar and increasingly complex.

Stephen R. Grand is a nonresident senior fellow at the Atlantic Council and a visiting professor at the Free University in Amsterdam.

Image: U.S. President Donald Trump participates in a signing ceremony for the U.S.-Korea Free Trade Agreement with South Korean President Moon Jae-in on the sidelines of the 73rd United Nations General Assembly in New York, U.S., September 24, 2018. REUTERS/Carlos Barria