THESE FIRST three characteristics relate to a fourth marker of the evolving international system: an intensification of global disorder. Throughout the post–Cold War era, U.S. policymakers feared that bipolarity’s end would unleash new or previously repressed forms of upheaval. And although that era has ended, we now see not an abatement, but an exacerbation of upheaval. As Hedley Bull wrote in The Anarchical Society, international politics features the continual clash between the forces of order and disorder. Today, due to factors ranging from rapid technological change to the disruptions caused by globalization, the agents of disorder seem more empowered than at any time in decades.

That empowerment is evident in phenomena that might otherwise seem unconnected. Take the emergence of super-spoilers—actors that cannot remake the international order, but can disrupt it fundamentally. North Korea now boasts an increasingly robust nuclear arsenal and is doggedly building an intercontinental delivery capability, controlled by an alarmingly bellicose leadership. Pyongyang is thus developing continually greater ability to underwrite its perpetually provocative behavior, and to threaten its opponents in the region and beyond with greater damage than ever before. Then there is the Islamic State. Although its military fortunes are in decline, the Islamic State has shown unprecedented ability, among nonstate actors, to foster chaos in a crucial geopolitical region, to master the use of technology for propaganda and recruiting purposes and to command or inspire acts of violence around the globe. Concern with rogue actors is nothing new, but not since Saddam Hussein’s defeat in 1991 have the rogues been so capable of profound geopolitical disruption as they are today.

The rise of the Islamic State also illuminates another aspect of intensifying disorder, which is that contemporary instability is now manifesting itself on a scale not seen for many years. To say that today’s Middle East is in crisis is a laughable understatement; the region is suffering a generalized breakdown of order comparable to what befell Europe during the Thirty Years’ War. Military conflicts are raging in the Arabian Peninsula, Iraq, the Levant and Libya; violent instability flourishes nearly from one end of the region to the other. The traditional authoritarian Arab state model has been undermined in some countries and collapsed in others; international borders have been rendered irrelevant. Whether—let alone when—the Middle East will be put back together is anyone’s guess; in the meantime, Middle Eastern instability has spread to neighboring areas such as Europe, with refugee flows and terrorist attacks having profound political and security effects.

A final manifestation of intensified global disorder is the proliferation of issues that are increasingly difficult to address through existing international fora. In recent years, global governance has worked fairly well on some issues—addressing the 2007–8 financial crisis, or suppressing piracy off the Horn of Africa. But on other issues, from the threats posed by cyberespionage and cyberwarfare, to the dilemmas of reconciling state sovereignty to the protection of human rights, to the challenges of making globalization work for communities that often feel themselves battered by impersonal economic and technological forces, the complexity of transnational problems seems to be outpacing the capacity of extant institutions. All of these issues contribute to an international environment in which instability has taken on alarming dimensions. And if it was hard enough for the international community to address such issues amid great-power comity, it is now harder still amid surging great-power competition.

Compare the painfully slow, but ultimately effective, international response to ethnic cleansing in Bosnia during the 1990s with the utterly ineffective efforts to address a greater catastrophe in Syria today. In the former case, U.S. dominance and decent relations with Russia made possible international consensus on the need to use force in Bosnia, and Moscow even participated in the subsequent NATO-led peacekeeping mission. In the latter case, resurgent Russian rivalry with Washington has consistently frustrated efforts to bring the Syrian Civil War to an end.

Great-power conflict has also complicated efforts to develop international norms regarding cyberspace. In fact, as demonstrated by aggressive Russian and Chinese hacking of U.S. systems—including Moscow’s effort to influence the 2016 presidential election—cyberspace has become an arena for geopolitical rivalry. The contested nature of the new global politics is exacerbated by the fact that the sources of today’s international upheaval often exacerbate one another.

THAT UPHEAVAL, in turn, is magnified by a fifth characteristic of contemporary global politics: pronounced uncertainty about the willpower of the chief defenders of the post–Cold War system.

The European allies, for instance, have long represented America’s most crucial partners in upholding international stability, yet Europe is now experiencing a profound systemic crisis. The fate of the European Union—and thus the basic cohesion of Europe—is uncertain at best, in view of Brexit and the anti-integration sentiment roiling countries from the Black Sea to the Atlantic. Beneath a veneer of unity, geopolitical divisions are also increasing. Countries like Greece and Italy urge a return to normalized relations with Russia; polling indicates that populations in many NATO member countries are unenthusiastic about defending the alliance’s easternmost members if they are attacked. Illiberal movements are on the rise, tarnishing Europe’s image as a bulwark of democratic values. Stagnant economies and excessive government debt are sapping the vitality of many European societies. Whether the European project is unraveling is hard to say, but Europe’s capacity to exert a stabilizing influence in a more ominous international environment has surely been undermined. And meanwhile, U.S. leadership is also facing its greatest crisis in decades.

That crisis has deeper origins than many observers realize. There was always likely to be a certain ennui with American globalism after the Cold War, for the threat that had originally catalyzed that globalism—the Soviet Union—had vanished. That ennui temporarily retreated before the missionary zeal that followed 9/11, but it returned with a vengeance after two frustrating wars. Barack Obama called for a return to nation building at home, and by 2013, 52 percent of Americans, the highest share in decades, thought that the country should “mind its own business internationally and let other countries get along the best they can on their own.” More recently, of course, the crisis of American leadership has been manifested in the election of a president who has assiduously stoked domestic grievances with globalization, and who has framed America’s traditional international responsibilities as sucker bets that have allowed other nations to enrich themselves at Washington’s expense. What Donald Trump’s rise thus augurs, in the eyes of many American internationalists, is not a return to isolationism, but a retreat from the idea that Washington should bear the primary burdens of global stability and prosperity, because doing so serves its own interests as well.

Predictions of such an American retreat have been proven wrong before, of course, and they may be proven wrong again. But there is now deep uncertainty about U.S. policy, and that uncertainty is itself destabilizing. It may promote hedging by U.S. allies who no longer believe that America’s security commitments are ironclad; it may provoke sharper challenges from aggressors who assess that the restraining forces arrayed against them are no longer so purposeful or unified. It may hasten the decay of liberal institutions like the EU and compound the stresses on the global trading system. Most broadly, if Washington behaves more erratically in global affairs—and there are already signs of this, such as Trump’s withdrawal from the Trans-Pacific Partnership and the Paris climate accord, and his berating of traditional U.S. allies—then the perception of U.S. steadiness that has underpinned the international order could be eroded. A period of growing turmoil is a bad time to stoke uncertainty about America’s traditionally stabilizing global role, but this is just what is happening today. The effects on international politics are unlikely to be either trivial or benign.

“THE CURRENT international environment is in turmoil,” Kissinger wrote in 1969, “because its essential elements are all in flux simultaneously.” This diagnosis is just as apt today. U.S. officials will encounter myriad crises in the coming years, on issues from great-power relations to nuclear proliferation to counterterrorism. Yet underlying these challenges is the fact of an international system undergoing profound structural change. The international order is being shaken by declining U.S. and Western overmatch, resurgent geopolitical revisionism and ideological conflict, intensified global disarray, and sharpening questions about the future of U.S. and European leadership. During the post–Cold War era, the primary—and generally positive—characteristics of international affairs were mutually reinforcing; today, these destabilizing factors are now compounding one another’s adverse effects.

Each of the issues identified here will be difficult enough to resolve on its own; positioning America to grapple effectively with the combination of structural changes at work today will be a task extending beyond any single presidency. That work should begin from three preliminary observations.

First, it would be a grave mistake to try to evade the current challenges by retreating into a “Fortress America” mentality. It is still premature to say which of the trends described here will ultimately prove to be transient, and which will become lasting elements of international politics. Moreover, a U.S. withdrawal would hardly mitigate the growing disorder; it would simply exacerbate the disruptive trends and increase the prospect that those trends would eventually reach out and touch America itself. Finally, the United States retains many comparative strengths over its adversaries and challengers, and those strengths still give it an enormous—albeit somewhat reduced—capacity to shape the international system. It is the art of statesmanship for policymakers to maximize the nation’s advantages and exploit its adversaries’ weaknesses. Doing so requires a prior commitment to actively influencing global affairs rather than retreating from them.