The U.S. alliance system: there’s never been anything quite like it. Ancient Athens helmed the Delian League. German Chancellor Otto von Bismarck skillfully played Europe’s alliance game in the nineteenth century. The coalitions that won the world wars were nearly global in scope. But no peacetime alliance network has been so expansive, enduring, and effective as the one Washington has led since World War II. The U.S. alliance system has pacified what once were killing fields; it has forged a balance of power that favors the democracies.

Yet the existence—and achievements—of that system may actually make it harder for Americans to understand the challenge they now confront. Across the Eurasian landmass, Washington’s enemies are joining hands. China and Russia have a “no-limits” strategic partnership. Iran and Russia are enhancing a military relationship that U.S. officials deem a “profound threat” to the “whole world.” Illiberal friendships between Moscow and Pyongyang, and Beijing and Tehran, are flourishing. Americans may wonder if these interlocking relationships will someday add up to a formal alliance of U.S. enemies—the mirror image of the institutions Washington itself leads. Whatever the answer, it’s the wrong question to ask.

When Americans think of alliances, they usually think of their own alliances—formal, highly institutionalized relationships among countries that are linked by binding security guarantees as well as genuine friendship and trust. But alliances, as history reminds us, can serve many purposes and take many forms.

Some alliances are nothing more than nonaggression pacts that allow predators to devour their prey rather than devouring one another. Some alliances are military-technological partnerships in which countries build and share the capabilities they need to shatter the status quo. Some of the world’s most destructive alliances featured little coordination and even less affection: they were simply rough agreements to assail the existing order from all sides. Alliances can be secret or overt, formal or informal. They can be devoted to preserving the peace or abetting aggression. An alliance is merely a combination of states that seeks shared objectives. And relationships that seemed far less impressive than today’s U.S. alliances have caused geopolitical earthquakes in the past.

That’s the key to understanding the relationships among U.S. antagonists today. These relationships may be ambiguous and ambivalent. They may lack formal defense guarantees. But they still augment the military power revisionist states can muster and reduce the strategic isolation those countries might otherwise face. They intensify pressure on an imperiled international system by helping their members contest U.S. power on many fronts at once. And were U.S. antagonists to expand their cooperation in the future—by sharing more advanced defense technology or collaborating more extensively in crisis or conflict—they could upset the global equilibrium in even more disturbing ways. The United States may never face a single, full-fledged league of villains. But it wouldn’t take an illiberal, revisionist version of NATO to cause an overstretched superpower fits.

AMERICA’S EXCEPTIONAL ALLIANCES

Alliances are shaped by their circumstances, and U.S. alliances—namely, NATO and Washington’s Indo-Pacific alliances—are products of the early Cold War. Back then, the United States faced the dual dilemma of containing the Soviet Union and suppressing the tensions that had twice ripped the Western world apart. The contours of U.S. alliances have always reflected these founding facts.

For one thing, U.S. alliances are defensive pacts meant to prevent aggression, not perpetrate it. Washington originally structured its alliances so their members could not use them as vehicles for territorial revanchism; when American alliances have expanded, they have done so with the consent of new members. U.S. alliances are also nuclear alliances: since the only way a distant superpower could check the Red Army was to threaten nuclear escalation, issues of nuclear strategy have dominated alliance politics from the outset. For related reasons, U.S. alliances are asymmetric. Washington has long shouldered an unequal share of the military burden, especially on nuclear matters, to avoid a scenario in which countries such as Germany or Japan might destabilize their regions—and terrify their former victims—by building full-spectrum defense capabilities of their own.

This point notwithstanding, U.S. alliances are deeply institutionalized: they feature remarkable cooperation and interoperability developed through decades of training to fight as a team. U.S. alliances are also democratic; they have survived for so long because their foremost members have a shared, enduring stake in preserving a world safe for liberalism. Finally, U.S. alliances are sanctified in written treaties and public pledges of commitment. That’s natural, because democracies cannot easily make secret treaties. It’s also vital because the beating heart of every U.S. alliance is Washington’s promise to aid its friends if they are attacked.

These features have made U.S. alliances tremendously attractive, effective, and stabilizing—which is why Europe and East Asia have been so peaceful since World War II and why Washington has more trouble keeping prospective members out than luring them in. But they also influence Americans’ views of alliances in ways that aren’t always helpful in understanding the modern world. After all, there is no rule that alliances must look like Washington’s—and some of history’s most pernicious alliances have not.

THE PREDATORS’ PACTS

Today isn’t the first time the world’s most aggressive states have made common cause. During the mid-twentieth century, an array of revisionist powers forged malign combinations to aid their serial assaults on the status quo.

In 1922, a still democratic Weimar Germany and the Soviet Union signed the Rapallo Pact, which promoted cooperation between these two losers of World War I. Between 1936 and 1940, fascist Italy, Nazi Germany, and imperial Japan inked agreements culminating in the Tripartite Pact, a loose alliance committed to achieving a totalitarian “new order of things” around the world. Along the way, Berlin and Moscow sealed the Molotov-Ribbentrop Pact, a nonaggression treaty that included protocols on trade and the division of Eastern Europe. And after a hot war gave way to the Cold War, Soviet leader Joseph Stalin and Chinese leader Mao Zedong negotiated a Sino-Soviet alliance that linked the two communist giants in their fight against the capitalist world.

These were some of history’s most dysfunctional, ill-fated partnerships. In several cases, they were temporary truces between deadly rivals. In no case was there anything like the deep cooperation and strategic sympathy that distinguish U.S. alliances today. This isn’t surprising: regimes as vicious and ambitious as Adolf Hitler’s Germany, Stalin’s Soviet Union, and Mao’s China shared little more than a desire to turn the world on its head. Yet this history is valuable because it shows how even the most transitory, tension-ridden partnerships can rupture the existing order, generating strong pressures in support of aggressive designs.

The Rapallo Pact was no full-fledged alliance: it was principally a détente in Eastern Europe, the region into which both Germany and the Soviet Union hoped to eventually expand. But the pact and the secret protocols that accompanied it turbocharged disruptive military innovation by international outcasts—Germany especially. At sites hidden within the Soviet interior, Germany began developing the tanks and planes the Treaty of Versailles had denied it, as well as operational concepts it would later use to great effect. This covert partnership collapsed when Hitler took power, but not before giving him a vital, deadly head start in Europe’s race to rearm in the 1930s.

Other revisionist pacts lowered the costs of aggression by reducing the isolation its perpetrators might otherwise have faced. The Molotov-Ribbentrop Pact—the “new Rapallo” Hitler signed with Stalin on the eve of World War II—lasted less than two years. But during that period, it shielded Germany from the effects of the British blockade by giving it access to Soviet foodstuffs, minerals, and energy and by providing a conduit through which Hitler could access Japan’s growing empire in Asia. Molotov-Ribbentrop enabled Germany’s rampage through Europe by making much of Eurasia an economic hinterland for Berlin.

Molotov-Ribbentrop also enabled violent aggrandizement on one front by taming tensions on others; in this sense, it was a nonaggression treaty that encouraged world-shattering aggression. The pact set off World War II in Europe by assuring Hitler that he could fight Poland and the Western democracies without interference from the Soviet Union—and by setting off Soviet land grabs from Finland to Bessarabia by assuring Stalin that he could reorder his periphery without interference from Berlin. For two crucial years, Molotov-Ribbentrop made Europe a paradise for predators by freeing them from the threat of conflict with each other.

Revisionist pacts also backstopped aggressive behavior by creating solidarity in crises. The partnership between Nazi Germany and Italy was often uneasy. But during crises over Austria and Czechoslovakia in 1938, Hitler was emboldened, and France and the United Kingdom were hamstrung, by the knowledge that Italian leader Benito Mussolini—who had earlier opposed German expansion—now stood behind him. The Sino-Soviet alliance offers another example. After Chinese intervention in the Korean War in 1950, the United States had to pull its punches—refraining from striking targets in China, for instance—for fear of starting a fight with Moscow.

Finally, revisionist alliances created multiplier effects by battering the status quo on several fronts at once. After signing the Sino-Soviet pact, Stalin and Mao sealed a division of revolutionary labor—Beijing pushed the communist cause with new energy in Asia, and Moscow focused on Europe—that forced agonizing debates over resources and priorities in Washington. Yet even absent formal coordination, advances by one revisionist made opportunities for others. During the late 1930s, the United Kingdom hesitated to draw a hard line against Germany in Europe because it faced danger from Italy in the Mediterranean and Japan in Asia. The fascist powers helped one another simply by destabilizing a system suffering from too many threats.

THE NEW REVISIONIST PACTS

Cataloging the destruction caused by an earlier set of revisionist alliances provides insight into what really matters about the combinations taking shape today. These combinations are numerous and deepening. An ever-expanding Chinese-Russian partnership unites Eurasia’s two largest, most ambitious states. In Russia’s long-standing relationships with Pyongyang and Tehran, aid and influence now flow both ways. China is drawing closer to Iran, to complement its decades-old alliance with North Korea. For years, Pyongyang and Tehran have collaborated to make missiles and mischief. This isn’t a single revisionist coalition. It is a more complex web of ties among autocratic powers that aim to reorder their regions and, thereby, reorder the world.

These relationships profit from proximity. During World War II, vast distances across hostile oceans impeded cooperation between Germany and Japan. But Russia, China, and North Korea share land borders with one another. Iran can reach Russia via inland sea. This invulnerability to interdiction facilitates ties among Eurasia’s revisionists—just as the war in Ukraine pushes them closer together by making Russia more dependent on, and willing to cut deals with, its autocratic brethren.

These relationships have their limits. Of the Eurasian revisionists, only China and North Korea have a formal defense treaty. Military cooperation is expanding, but none of these partnerships remotely rival NATO in interoperability or institutionalized cooperation. That’s partly because historical tensions and mistrust are pervasive: as one example, China still occasionally claims territory Russia considers its own. But even so, revisionist collaborations are producing some familiar effects.

Take, for example, the way that Chinese-Russian collaboration is turbocharging disruptive military innovation. Although China has been under Western arms embargoes since 1989, its record-breaking military modernization has benefited from purchases of Russian aircraft, missiles, and air defenses. Today, China and Russia are pursuing the joint development of helicopters, conventional attack submarines, missiles, and missile-launch early warning systems. Their cooperation increasingly includes shadowy coproduction and technology-sharing initiatives rather than simply the transfer of finished capabilities. If the United States one day fights China, it will be fighting a foe whose capabilities have been materially enhanced by Moscow.

Meanwhile, Russia’s defense technology relationships with other Eurasian autocracies are flourishing. Iran has sold Russia missiles and drones for use in Ukraine, even helping it build facilities that can produce the latter at the scale modern war demands. Russia, in exchange, has reportedly committed to delivering advanced air defenses, fighter aircraft, and other capabilities to Iran that could change the balance in the ever-contested Middle East. As in the Rapallo era, revisionist states are helping each other build up the military power they need to tear down the status quo.

Revisionist alliances are also—once again—making aggression less costly by mitigating the strategic isolation aggressors might otherwise face. Despite Western sanctions and horrific military losses, Russia has sustained its war in Ukraine thanks to the drones, shells, and missiles Tehran and Pyongyang have provided. Russian President Vladimir Putin’s economy has stayed afloat because China has absorbed Russian exports and provided Moscow with microchips and other dual-use goods. Just as Hitler once relied on Eurasian resources to thwart the British blockade, Putin now relies on China to blunt the economic harms of confrontation with the West. Expect more of this, as the revisionists cultivate networks—whether the International North-South Transport Corridor connecting Iran and Russia or the Eurasian commercial and financial bloc Beijing is constructing—to keep their commerce beyond Washington’s reach.

These relationships, additionally, are maximizing the risk of violent instability on some frontiers by minimizing it on others. The Chinese-Russian border was once the world’s most militarized. Today, however, a de facto nonaggression pact has freed Putin from the threat of conflict with China, allowing him to hurl nearly his entire army at Ukraine. China, too, can push harder against U.S. positions in maritime Asia because it has a friendly Russia to its rear. Beijing and Moscow don’t need to fight shoulder to shoulder, as Washington does with its allies, if they fight back to back against the liberal world.

The same friendships are delivering another disruptive benefit by increasing the prospect of autocratic solidarity in crises. For decades, North Korea’s alliance with China has constrained Washington from responding more firmly to its provocations. More recently, North Korean leader Kim Jong Un’s increasing belligerence may be fueled by an expectation (warranted or not) that Putin will have his back. Likewise, in a future showdown over Iran’s nuclear program, Tehran’s booming military partnership with Moscow could give it stronger diplomatic support—and better arms—with which to resist. China and Russia, for their part, are conducting military exercises in potential conflict zones from the Baltic to the western Pacific. These activities may be meant to signal that one revisionist power won’t simply sit on the sidelines as Washington deals with another.

Not least, the revisionists enjoy a perverse symbiosis by weakening the international order from several directions at once. Russia is brutalizing Ukraine and threatening eastern Europe, as Iran and its proxies sow violent disorder across the Middle East. China grows more menacing in the Pacific, as North Korea drives its missile and nuclear programs forward. All this creates a pervasive sense that global order is eroding. It also poses sharp dilemmas for Washington: witness U.S. debates over Ukraine versus Taiwan, today’s actual wars versus tomorrow’s prospective ones. As during the 1930s, Eurasia’s autocracies help one another by overtaxing their common foe.

TROUBLE TO COME

American analysts still sometimes refer to relationships among U.S. adversaries as “alliances of convenience,” the implication being that clever diplomacy can precipitate a divorce. That’s unlikely to happen any time soon. The Eurasian autocracies are united by illiberal governance and hostility to U.S. power. If anything, growing international tensions are giving them stronger reasons for mutual support. Indeed, a Russia that remains isolated from the West will have little choice but to lean into partnerships with China, Iran, and North Korea. The United States may be able, periodically, to slow this process—as it did in 2022–23 by threatening China with harsh sanctions if it gave Russia lethal aid in Ukraine—but it probably can’t reverse the larger trend. And even if today’s revisionist ties never amount to a full-blown Eurasian alliance, they could plausibly evolve in ways that would strain U.S. power more severely.

More sensitive cooperation could make for more startling military breakthroughs. Russian technology will reportedly figure in China’s next-generation attack submarine, albeit through a process of “imitative innovation” rather than direct transfer. If Russia someday provides China—whose subs are still noisy and vulnerable—with state-of-the-art quieting technology, it could undercut U.S. advantages in one domain in which Washington still has outright supremacy over Beijing. Likewise, South Korean officials fear the payoff for North Korea’s arms shipments to Russia might be Russian aid to North Korea’s space, nuclear, and missile programs—which could help those programs advance faster than U.S. analysts expect. More broadly, as military cooperation morphs into coproduction or technology transfers, as opposed to the sale of finished weapons, it becomes harder to monitor—and increases the chances of capability jumps that catch outside observers off-guard.

Eurasia’s revisionists could create further dilemmas by cooperating more closely in crises. If Russia deployed naval forces in the East China Sea amid high U.S.-Chinese tensions—or if Moscow and Beijing sent vessels to the Persian Gulf during a crisis between Iran and the West—they could make the operational theater more complicated for U.S. forces, raising the risk that a fight with one might trigger unwanted escalation with others. The revisionist powers could even aid one another in outright war.

In a U.S.-Chinese conflict, Russia could conduct cyber-operations against U.S. logistics and infrastructure to make it harder for Washington to mobilize and project power. One revisionist power could fill critical capability gaps, whether by resupplying a friend when key munitions run low or—as China has done in Ukraine—providing vital components that don’t quite qualify as “lethal” aid. Or it might posture forces in threatening ways. During a fight between the United States and China, Russia would only have to move forces menacingly toward eastern Europe to make Washington account for the likelihood of conflicts on two fronts.

The Eurasian autocracies surely don’t wish to die for one another. But they presumably understand that a crushing American victory over one would leave the remainder more vulnerable. So they might try to help themselves by helping one another—if they can do so without plunging directly and overtly into the fight.

THINKING AHEAD

Ties between Eurasian revisionists may not look like alliances as Americans typically understand them, but they have plenty of alliance-like effects. This isn’t an entirely bad thing for Washington: the closer U.S. antagonists get, the more one’s bad behavior tarnishes the others. Since 2022, for instance, China’s image in Europe has suffered because Beijing tied itself so closely to Putin’s war in Ukraine. The opportunity, then, is to use adversary alignment to accelerate Washington’s own coalition-building efforts, just as the United States used the blowback from Russia’s invasion to induce greater European realism about China. Doing so will be critical, because today’s revisionist pacts are increasing the freedom of action U.S. rivals enjoy and the capabilities they wield. The United States must get used to a world in which the links among its rivals magnify the challenges that they individually and collectively pose.

This is an intellectual and analytical challenge as much as anything else. For example, the United States may need to revise assessments of how long its adversaries will take to reach key military milestones, given the help they are receiving—or could receive—from their friends. Washington must also rethink assumptions that it will face adversaries one-on-one in a crisis or conflict and account for the aid—covert or overt, kinetic or nonkinetic, enthusiastic or grudging—other revisionist powers could render as tensions escalate. The United States especially needs to wrestle with the risk that adversary relationships will promote a certain globalization of conflict—that the country could end up facing multiple, interlocking regional struggles against adversaries that cooperate in important, sometimes subtle ways.

Finally, U.S. officials should consider how these rivals’ partnerships could evolve in unexpected or nonlinear ways. Recent history is instructive. Although the Chinese-Russian strategic relationship has arisen over decades, that relationship—to say nothing of Moscow’s ties to Pyongyang and Tehran—has ripened considerably during the war in Ukraine. How might a future crisis over Taiwan, which triggers sharp U.S. sanctions on China, affect Beijing’s cost-benefit analysis regarding a still deeper alliance with Russia? Or how might a more thorough breakdown of order in one region tempt revisionist powers to intensify their campaigns in others?

Thinking through such scenarios is, unavoidably, an exercise in speculation. It is also an intellectual hedge against a future in which relationships—many of which have already exceeded U.S. expectations—continue to develop in disturbing ways. In the years ahead, the challenge of adversary alignment may well be inevitable. The degree to which it surprises is not.