Meanwhile, the relative positions of America’s principal competitors have improved significantly. Russian economic power remains unimpressive, but an aggressive military modernization program has roughly doubled defense spending over a decade while also developing the capabilities needed to compete with the West—airborne assault units, special-operations forces, ballistic and other missile systems, and anti-access/area-denial capabilities, among others. China, meanwhile, has expanded its share of global wealth more than threefold, from 3.3 to 11.8 percent, between 1994 and 2015, and its share of world military spending more than fivefold, from 2.2 to 12.2 percent. As in Russia’s case, China’s military buildup has featured the tools—ballistic and cruise missiles, diesel-electric and nuclear submarines, advanced air defenses, and fourth-generation fighters—needed to offset longstanding U.S. advantages in the Asia-Pacific, as well as capabilities, such as aircraft carriers, needed to project Chinese power even further afield. The uncontested U.S. primacy of the 1990s has become the highly contested primacy of today.

This is no academic distinction; the pernicious effects of this shift are already being seen. The decline of allied military power has made it harder for those allies to defend themselves against growing security threats, and to make more than token military contributions to addressing global challenges such as the rise of the Islamic State. Secretary of Defense Robert Gates famously warned in 2011 that NATO faced a “dim if not dismal future” if European capabilities continued to erode; American frustration has only become more pronounced since then. More fundamentally still, the changing power balance means that U.S. rivals and adversaries now have greater ability to shift the international order to suit their own preferences, a factor driving a second key shift in global politics today.

IF GREAT-POWER comity was the post–Cold War norm, great-power competition is the standard today. Authoritarian rivals that were never fully reconciled to the post–Cold War order, and accepted it only to the degree compelled by U.S. and Western primacy, are now using their greater relative power to push back against that order in key geopolitical regions from East Asia to the Middle East to eastern Europe. Because Washington’s principal adversaries can concentrate their resources regionally, rather than having to distribute them globally, the power shifts that have occurred in recent years are having outsized effects at the regional level. And because the regional orders now being challenged have been the foundation of the broader post–Cold War system, these countries are effectively subverting the system “from the bottom up.”

Consider Chinese behavior in East Asia. Chinese leaders always saw America’s post–Cold War dominance as a transitory condition to be suffered for a time, not something to be welcomed forever. And so as China’s geopolitical potential has soared, Beijing has taken bolder steps to erect a Sino-centric regional order. It has asserted expansive maritime claims and used techniques such as island building to shift facts on the ground without risking a premature military clash with America. It has challenged longstanding norms such as freedom of navigation in the South China Sea, and steadily increased efforts to coerce its neighbors. It has probed and worked to weaken U.S. alliances and partnerships, by simultaneously wooing and intimidating America’s regional friends. Finally, Beijing has conducted a major military buildup focused precisely on capabilities that will give it dominance over its neighbors and prevent the United States from intervening in their defense.

These efforts are now having an accumulating effect. Chinese coercion has dramatically altered perceptions of momentum and power in the region, while the Chinese buildup has made the outcome of a Sino-American war over Taiwan or other regional hotspots far more doubtful. Chinese economic diplomacy has drawn many countries in the region closer into Beijing’s economic orbit. “America has lost” the struggle for regional supremacy, President Rodrigo Duterte of the Philippines announced in 2016—an exaggeration, surely, but a marker of how contested the region has become.

Great-power competition is even more unvarnished in Europe, where a militarily resurgent Russia is reasserting lost influence and undoing key aspects of the post–Cold War settlement. Moscow has waged wars of conquest against Georgia and Ukraine; it has worked to undermine NATO and the European Union through efforts ranging from paramilitary subversion, to military intimidation, to financial support for anti-EU and anti-NATO politicians and other intervention in Western political processes. In doing all of this, Russia has fundamentally contested the notion of a post–Cold War Europe whole, free and at peace; it has challenged—with some success—the institutions that have long maintained security and prosperity in the region. And as with China, these actions have been underwritten by a military buildup that has restored Russian overmatch along NATO’s exposed eastern flank and enhanced Moscow’s ability to project power as far afield as the Middle East. Russia has become an ambitious great power again: it is asserting its prerogatives in ways that only seem anomalous in contrast to the remarkable cooperation of the post–Cold War era.

Finally, geopolitical revisionism is alive and well in the Middle East. Iran is not in the same power-political class as Russia or China, but it is a regional power seeking to assert regional mastery. It is doing so via the use of proxies and its own forces in conflicts in Syria, Yemen and Iraq, via the weaponization of sectarianism in countries across the region, and via investments in asymmetric capabilities such as ballistic missiles and special-operations forces. This agenda has led Tehran into conflict with U.S. security partners such as Egypt, Saudi Arabia and the United Arab Emirates; it has contributed significantly to the instability that plagues the region.

Each of these geopolitical challenges is different, of course. But taken collectively, they represent a geopolitical sea change from the post–Cold War era. The revival of great-power competition entails sharper international tensions than have been known for decades, and the return of Cold War phenomena such as arms races and security dilemmas. It entails intensifying conflicts over the global rules of the road, on issues from freedom of navigation in the South China Sea to the illegitimacy of altering borders by force. It entails starker struggles over states that reside at the intersection of rival great powers’ spheres of influence, such as the Philippines, Ukraine and Iraq. Finally, it raises the prospect that great-power rivalry could lead to great-power war—a phenomenon that seemed to have followed the Soviet Union onto the ash heap of history with the end of the Cold War. The world has not yet returned to the titanic geopolitical struggles of the twentieth century, but it is returning to the historical norm of great-power strife—with all the dangers that entails.

AS GREAT-POWER competition has returned, so has global ideological struggle. If the post–Cold War era featured a widespread assumption that the dominance of the liberal political-economic model was incontestable, the current era is seeing the revival of authoritarian challenges and the reemergence of ideological differences as a driver of geopolitical conflict. Today’s world is rife not just with geopolitical revisionism, but with ideological revisionism as well.

To begin with, the spread of democracy has stalled. Between 1974 and 2000, the number of electoral democracies tripled, from thirty-nine to 120. Yet the number of electoral democracies has remained roughly stagnant since then, and in every year since 2006 more countries have experienced declines in freedom than increases. From the rise of antidemocratic leaders in Venezuela and Turkey, to the erosion of democratic norms within NATO countries such as Poland and Hungary, democracy’s travails are an increasingly global phenomenon.

Authoritarian models, meanwhile, are making a comeback. Tenacious dictators have mobilized the power of technology to better monitor and repress dissent. Moreover, the economic and social difficulties many democracies have encountered in recent years have created an opening for unabashedly authoritarian leaders. Hungary’s Viktor Orban made global headlines in 2014 when he castigated the debilities of liberal society and declared the ascendancy of the “illiberal state.” Likewise, powerful authoritarian states are assiduously working not just to repress internal challenges, but to thwart and reverse democracy’s advance overseas. Russia and China are supporting besieged authoritarian regimes, while also resisting efforts to punish gross human-rights violations through the United Nations. In recent years, in fact, all three of America’s major geopolitical competitors—Russia, Iran and China—have joined forces to support Bashar al-Assad’s murderous regime in Syria, through measures ranging from intelligence and economic support to full-on military intervention. The end of history has ended; the global ideological battle has been joined once more.

That ideological battle, in turn, has reemerged as a marker and cause of great-power rivalry. The United States and its largely democratic allies increasingly find themselves in conflict with revisionist authoritarian governments in Russia and China. This is no coincidence. Opposing domestic political structures fuel mutual mistrust; they create differing visions of what type of international order is legitimate and desirable. Washington has long sought a world full of democracies, and it has viewed the persistence of powerful authoritarian states as an affront to that project. Russian and Chinese leaders are desperate to make the world safe for authoritarians, and view U.S. foreign policy as a menace to that project. A great hope of the post–Cold War world was that ideological convergence would lead to greater geopolitical harmony. Alas, today ideological struggle and great-power conflict increasingly go hand in hand.