The Long Unipolar Moment?

The End of the American Era

Joshua Shifrinson

In “The Myth of Multipolarity” (May/June 2023), Stephen Brooks and William Wohlforth challenge the idea that the United States is in free fall down the great-power ranks. Washington, they say, “remains at the top of the global power hierarchy—safely above China and far, far above every other country.” In their view, the world “is neither bipolar nor multipolar, and it is not about to become either.”

The authors are correct that the United States is still the most powerful country in the world. But their basic argument—that the current distribution of power is unipolar—is off. In fact, a closer look at the authors’ preferred indicators of power and their underlying assumptions suggests just the opposite. Unipolarity is an artifact of the past.

Brooks and Wohlforth base their argument on three fundamental claims. One is that the crude distribution of power—or a country’s overall economic and military capabilities—shows that the United States and China are the only two plausible great powers today. The second is that the United States’ technological advantages, combined with the high barriers China must surmount to catch up, mean that China is not a peer competitor. The authors’ final claim is that the international system lacks meaningful balancing against the United States, as other states have neither created formal alliances nor armed themselves in ways that constrain U.S. freedom of action. In bipolar and multipolar systems, they contend, the poles engage in pervasive balancing against each other, so the current dearth of balancing suggests that unipolarity endures.

But each of these points is suspect. For one thing, requiring that other powers have rough parity with the leading state is a strange way to define or count poles. Throughout history, great powers have never been thought of as quantitative peers. Rather, they are states with sufficient economic and military resources, diplomatic reach, and political acumen to influence other leading countries’ calculations in peace and make a good showing against them in war. This broader definition is why the Austro-Hungarian Empire, imperial Japan, and the Soviet Union have all been judged as “poles” of their respective international systems. Even though each of these states was far weaker than the strongest state of the time, they were still capable enough to factor mightily into questions of war and peace.

Ultimately, there is a threshold—sometimes significantly lower than one might expect based on crude measures—reflecting how states compare across the board in their economic, military, technological, and diplomatic attributes, and above which states qualify as poles. Polarity, after all, captures those state attributes that allow some of them to influence the course of world politics on core matters. And although overall economic and military output matter, they take analysts only so far in judging power. Today, a diverse economy, a favorable geographic position, and the possession of nuclear weapons are especially important factors in such assessments. India, for example, with its large economy, favorable geography, and strong nuclear arsenal, gets a boost relative to crude power measures. So does Japan, which has almost all the same advantages as India, albeit with a latent nuclear capability. China, meanwhile, merits a similar—and perhaps even greater—boost, with its less favorable geography offset by its impressive conventional military and growing nuclear arsenal.

Nor is China’s relative technological backwardness nearly as much of an impediment to its great-power status as Brooks and Wohlforth allege. Putting aside questions about how difficult it is for countries to develop cutting-edge technology, countries do not need to be technological leaders to qualify as leading powers. Austria-Hungary and Russia, for instance, were backward by the standard of 1914, yet they were central to European multipolarity. The United Kingdom failed to leverage the second Industrial Revolution in the late nineteenth and early twentieth centuries to the extent that Germany did, but it was still a pole in the same era. The Soviet Union was never close to net technological parity with the United States, but it was considered a peer competitor throughout the Cold War.

Judging power is a fraught game.

Instead, what a country needs is to produce a sufficient quantity of “good enough” technological material to influence major international decisions. On this score, it is notable how far China has come in a short period. The country had almost no domestic computer industry in the late 1980s, but today China is a major producer of the computer chips that run much of the global economy. The same is true in other fields. It is thus unsurprising that U.S. policymakers are increasingly worried about China’s technological prowess: given that China is producing a lot of good (if not great) material, it is not clear that the United States’ technological lead would be decisive if the two states went to war.

In fact, the United States appears to have its hands full with China as is. Brooks and Wohlforth are right that any one country can be balanced by the United States more readily than the reverse. Yet it is the existence of balancing, rather than its intensity, that tells us about the distribution of power. This distinction is important because Washington’s own behavior indicates that the United States faces growing geopolitical constraints and counterbalancing pressures, all of which imply that the system is not unipolar. Despite a defense budget approaching $1 trillion, policymakers and experts routinely argue that China’s growing economic and military footprint means that the United States can no longer simultaneously meet its commitments in Asia, Europe, and the Middle East. The result has been many fraught conversations over where and how Washington should spend its finite resources. Meanwhile, the United States is redoubling its efforts to enlist India, Japan, and other Asian countries against China. Such efforts would not take place if the world were still dominated by Washington—and by Washington alone.

Judging power is a fraught game. Yet Brooks and Wohlforth’s claims are exceedingly difficult to square with both U.S. policy today and a more comprehensive view of what constitutes a great power. Analysts can debate whether the world is bipolar or multipolar. But unipolarity is no more.

Beyond Poles

Anne-Marie Slaughter

I have a recurrent nightmare about global politics. At the end of this century, or even midway through it, life as we know it is forever transformed for the worse through a combination of flames, flood, disease, drought, famine, and continual conflict caused by hundreds of millions of migrants. And atop the ruined globe, Uncle Sam is waving a flag, declaring victory over China and insisting that the United States is still “number one.”

Brooks and Wohlforth’s article deepens my pessimism. It is as if they are writing in 1985 or 1945. They approach international politics as if it were a game of great powers, where the distribution of different kinds of power among various states determines the size, location, and tilt of the playing field. The point of their article is to demonstrate that the world remains unipolar, with the United States as the dominant pole, even if its measurable military and economic power has diminished relative to other countries. “The world is neither bipolar nor multipolar, and it is not about to become either,” they argue. But those who are dying from heatwaves and fleeing floods and fire might beg to differ. The world has two poles: north and south. The ice at both is melting rapidly, with untold dangers for all of us.

As the Biden administration’s 2022 National Security Strategy points out, existential “transnational” threats such as climate change, pandemics, and energy shortages exist side by side and on equal footing with the traditional geopolitical threats that Brooks and Wohlforth address. The distribution of power captured by unipolarity, bipolarity, or multipolarity is thus still a key background condition for officials to consider as they formulate policy.

The question, however, is what counts as a pole. And curiously, Brooks and Wohlforth seem to have determined that the answer is limited to states. They therefore write as if the European Union simply does not exist. That is a major omission. Even according to their own calculations, the EU is a major power. And it may be the one doing the most to stem existential risks.

STATE OF AFFAIRS

Brooks and Wohlforth offer a straightforward definition of multipolarity: a system in which the international order is “shaped largely by the three or more roughly matched states at the top.” At present, they write, “the United States and China are undoubtedly the two most powerful countries, but at least one more country must be roughly in their league for multipolarity to exist.” They then present two charts, one showing data on GDP and the other showing military spending, to demonstrate that the United States and China are far ahead of France, Germany, India, Japan, Russia, and the United Kingdom. The data, they argue, also show that the United States is far ahead of China.

Add the EU to these charts, however, and the authors’ claims become harder to support. According to the International Monetary Fund, the United States’ GDP is $26.9 trillion, China’s is $19.4 trillion, and the EU’s is $17.8 trillion. Among the other biggest economies are India and Japan, which both have GDPs between $3 and $5 trillion. The United States may be well ahead of its nearest competitors, but the top three global economies are an order of magnitude ahead of all the others.

The United States still far outpaces both China and the EU with regard to military spending. But the EU’s spending is in the same range as China’s: the European Defense Agency reported in December 2022 that the defense expenditures of the 26 EU member states that provided data totaled roughly $214 billion for 2021, compared with China’s $242 billion in 2022. Given the war in Ukraine, the EDA’s 2022 numbers will be substantially higher. Collaborative EU defense procurement is steadily rising (although it started from a very small base), and the EU is engaging in 12 civilian and nine military missions around the world under its Common Security and Defense Policy.

All in all, Brooks and Wohlforth’s argument is at its strongest when analyzing pure military power. The United States is indeed far ahead of other countries, spending three times as much as its nearest competitors. Still, if the United States had to support Ukraine against Russia or Taiwan against China without the European members of NATO or the EU at its side, Washington’s odds of success would be significantly diminished. As the war in Iraq demonstrated, the United States cannot simply command its allies to fight. NATO runs on the consent of its members, including important European powers. The EU plays an essential role alongside NATO in forging this consensus.

Brooks and Wohlforth are hardly alone in their insistence that only states count in calculations of international power. It is a view shared by the larger U.S. national security community, which consistently ignores and underestimates the EU. Yet the EU has many of the attributes of a state: a currency (which serves as the world’s second-largest reserve currency), lawmaking abilities, diplomatic representation, and a common foreign and security policy. And regardless of what kind of entity it is, the EU is an extremely powerful player. It is the world’s most influential regulator, a status that is ever more important as climate crises expand and multiply. It is the world’s leader in the transition to green energy. The EU’s economic aid kept Ukraine afloat between 2014 and 2022, and the bloc will provide the bulk of reconstruction funds after the war ends. And the EU’s sanctions against Russia are more significant than the United States’, given the bloc’s major trading relationships with its eastern neighbor.

Critically, the EU is a deeply stabilizing force. To see why, imagine the world without it. The bloc’s countries would still be military allies through NATO, but they might otherwise be economic competitors. China would have been able to move many eastern and southern European states into its orbit, as it was doing before Russia invaded Ukraine. And Moscow would have had a better chance of splitting European governments from one another. Some major EU countries, for instance, would have been far more reticent to reduce their dependence on Russian oil and gas, even during the Ukraine war, without the EU compromise machine.

UNDER THE INFLUENCE

The EU challenges analysts to rethink the definition of a state. But so did the United States when it was founded; the U.S. Constitution was designed to form “a more perfect union” among its member states. There are critical differences between the EU and countries such as the United States, of course. Australia, Canada, Germany, the United States, and many other countries are federated unions, ultimately subordinate to a national government, whereas the EU is a networked union that allows its members to act together in some ways and apart in others. The EU certainly has less power over its constituent parts than does the United States. Yet the EU still has far more power over its members, which remain sovereign states, than any other regional entity. It is one of a kind.

That may not be the case forever. In pioneering its networked form, the EU has developed a template that other regional organizations are following and customizing in various ways. The African Union, which replaced the Organization of African Unity in 2002, seeks increased social and economic integration for its continent. To better figure out how it can achieve this end, AU and EU ministers and commission members meet regularly. The Association of Southeast Asian Nations, established in 1967, was controlled almost entirely by networks of national ministers, with very little central authority. But in recent years, ASEAN has established more coordinating mechanisms, including a strong free trade agreement among its members. The body also created the ASEAN+3 forum—which includes China, Japan, and South Korea—through which all the members’ foreign affairs ministers discuss security issues.

Foreign policy practitioners should hope these blocs succeed. Powerful regional unions are the necessary intermediaries between international or global institutions and state and local governments. They will be essential to the world’s ability to meet global challenges that require the cooperation of all states (or at least the vast majority of states) to solve. Even the mighty United States will have to act in concert with Canada and Mexico to strengthen the resilience, biodiversity, health, and security of North America. This fact became readily apparent this summer, when the U.S. government sent firefighters to Canada to control wildfires, whose smoke was choking major American cities.

Brooks and Wohlforth might still dismiss regional blocs, even as those blocs aspire to become unions. In their article, the authors distinguish between mere influence—“the ability to get others to do what you want”—and power, which they suggest demands statehood and must be quantified. But this division is meaningless. Power has multiple components; influence is certainly one of them. Thankfully for the planet, and for humanity’s ability to address a variety of existential threats, the influence of institutions that balance sovereignty and unity will help determine the future.

Polarity Is What States Make of It

Bilahari Kausikan

Brooks and Wohlforth argue that the United States, though not as dominant as before, is still unquestionably at the top of the international order. Almost all the world’s “real alliances,” they contend, “bind smaller states to Washington, and the main dynamic is the expansion of that alliance system.”

These claims are correct but beside the point. The United States will, indeed, remain dominant in many, perhaps most, economic and military metrics for quite some time. Yet to conclude that multipolarity is a myth is to conceive of multipolarity in superficial, overly formalistic, and largely obsolete ways. For their part, Brooks and Wohlforth define the concept based on the experiences of the nineteenth and twentieth centuries by emphasizing formal alliances and hard measurements of power—such as a country’s military expenditures or gross domestic product—and ignoring everything else. But today, power depends as much on the way different states control critical resources, and how they informally collaborate, as it does on the size of formal alliances or military forces. And by these standards, the world is much more multipolar than Brooks and Wohlforth believe.

NO WAY OUT

The contemporary international system is characterized by a global web of supply chains of a complexity and density never seen before, one that links friend and foe alike and frequently makes that distinction ambiguous. The U.S.-Chinese rivalry and the war in Ukraine may have stressed this system, but aside from some specific technologies with national security implications, neither challenge has reversed globalization. Nor will they. The costs of abandoning interdependence are simply too high to be realistically entertained.

Some U.S. policymakers would like to see the United States and its allies separate their economies from China’s. But whatever their concerns about Beijing, no government, even the closest U.S. ally, will stop engaging with China, even as many states try to mitigate the risks of interdependence. The country is simply too big an economic actor. According to China’s official statistics, for example, the country accounted for about 30 percent of global manufacturing output in 2021, and there is a limit to how much any country, including the United States, can diversify away from what is in effect the factory of the world. (This statistic also indicates that China is highly dependent on exports, and so it, too, will have serious difficulty becoming more self-reliant.)

As Brooks and Wohlforth note, the United States has a far more powerful military and a larger economy than China does. But in today’s interconnected world, multipolarity no longer requires approximate military and economic symmetry. Any state that controls an important international resource or plays a significant international role in some domain cannot be dismissed as a bit player. For example, based on the size of its military or GDP, it is absurd to consider tiny Singapore any kind of global “pole.” But as a financial center, a port in global trade, and a critical hub for oil refining (even though it produces no oil), Singapore has a consequential international position. Larger states, such as Australia, India, Japan, Saudi Arabia, and South Korea, have even more global influence.

TWISTING IN THE WIND

Brooks and Wohlforth are right that the United States has no peer. No other country poses an existential threat to it. Russia is clearly a dangerous power, but it is in decline. China is a formidable competitor, but it is perhaps the biggest beneficiary of post–Cold War globalization and therefore has little incentive to kick over the table and seek radical new arrangements. And even if it wanted to, it is doubtful that China has the power to totally rewrite global rules. Beijing may want to dominate the international system in order to recover the position and status it believes it lost during a century or more of weakness, but those are different matters.

Still, the lack of an existential threat is not proof that, as the authors argue, multipolarity “will remain a distant eventuality.” Indeed, in the absence of an existential challenge, the United States has no strong reason to work to uphold international order—and therefore to try to maintain its leading position. As a result, since 1991, most administrations have looked inward and focused on domestic issues over international ones. This new emphasis has made even the closest U.S. allies and partners anxious about the strength of Washington’s global commitments, as has the highly polarized, and therefore unstable, nature of American domestic politics. Concerns about Chinese and Russian behavior may keep these governments clustered around Washington for now, but they cannot trust the United States to be the ally that it used to be. In the long term, U.S. friends and partners will likely seek more autonomy from Washington and greater flexibility in their relations with China, Russia, and other countries.

These countries will not, of course, abandon the United States. Washington will still be their primary partner. But in the twenty-first century, primacy and unipolarity are not the same thing. There are many ways to measure influence, so multipolarity has become as much a subjective as an objective phenomenon. It is defined mostly by how countries—regardless of their relationship with the United States—perceive their strategic choices and exercise their agency. When Washington withdrew from the Trans-Pacific Partnership, for example, the trade deal did not collapse. Instead, Japan took the lead in organizing a successor that features the rest of the TPP’s original members. China has since applied to join the trade bloc, and some members have suggested they are willing to let Beijing in. It is not hard to see why: they want further access to China’s market.

The international order is therefore indeed multipolar. Clusters of countries form, dissolve, and reconstitute themselves around different issues in order to promote their interests. Even on matters of great significance, no one state—not even the United States—can run the show.

The Ties That Bind

Robert Keohane

Brooks and Wohlforth are correct that the United States remains the most powerful country in the world. They are likely also right that China will not overtake it anytime soon.

But although their description of the world is largely correct, it is of limited use to policymakers—especially those focused on trying to prevent a U.S.-Chinese war. This frightening possibility would most likely arise from disagreements between China and the United States escalating into conflicts, not from a shift in the balance of power between the two countries. Analysts should therefore pay more attention to the characteristics of the U.S.-Chinese relationship than to whether the world is unipolar, bipolar, or multipolar. They must think about how the two states—and the states in their regions—are interdependent. And in the context of the U.S.-Chinese relationship, the very fact of interdependence creates the potential for conflict since the effective pursuit of each side’s interests affects the other side’s behavior.

As they monitor the contours of their countries’ relationship, American and Chinese policymakers should remember that Washington’s and Beijing’s interests, and thus the patterns of interdependence, are partly subjective. These are shaped as much by their perceptions of each other as by their material resources. The world may stumble into conflict even though one country still dominates.

MOVING PARTS

In Power and Interdependence, Joseph Nye and I argued that global power politics is defined not by the material resources held by various countries but by the characteristics of their relationships with each other. According to this conception, power in an interdependent relationship flows to the less dependent actor. “A less dependent actor in a relationship often has a significant political resource, because changes in the relationship will be less costly to the actor than to its partners,” we wrote. But the significance of asymmetrical interdependence with respect to a specific political resource—such as military capability, economic strength, or the appeal of a country’s values—varies depending on the nature of the relationship. And because relations between major powers are multidimensional, a country can have the advantage in one area while being subordinate in another. Yet which country has the advantage in which area is unlikely to become evident until the relationship is put under stress.

To understand how the power resources that Brooks and Wohlforth attribute to China and the United States affect these countries’ strategies and the likely outcomes of their interactions, analysts need to understand the multiple contexts that will affect how the two countries operate. In particular, they need to assess perceived conflicts of interest, whether institutions are in place to limit or manage conflict, how domestic politics intersect with geopolitical strategy, and the soft-power effects of great-power behavior.

On three of these four dimensions, the world is a much more dangerous place than it was 20 years ago. The perceived conflicts of interest between China and the United States have clearly become more severe since Xi Jinping became China’s president in 2013. In particular, China now seems to indicate more urgency in its desire to control Taiwan, and the United States has edged toward a firmer commitment to Taiwan’s defense. As China’s military power has grown during this time, its capacity to attack Taiwan has increased. The combination of increased Chinese ambition and increased Chinese power has raised the chances of a cross-strait war that could draw in the United States.

Power is contextual.

At the same time, U.S.-Chinese relations lack the searing memories of barely avoided nuclear war, the institutional guardrails, and the established patterns of restraint that characterized U.S.-Soviet relations for the years after the Cuban missile crisis in 1962. Domestic politics in both states are also growing more dangerous. In the United States, politicians of both parties have been competing to show how tough they can be on Beijing. In China, proponents of “Wolf Warrior” diplomacy—in which Chinese officials aggressively berate external critics—have become more active and appear to receive support from the country’s top leadership. The dangers of a competition in toughness are obvious: loud political voices are pushing in the same direction, creating political incentives for leaders to refuse compromise for fear of seeming weak. Only on the soft-power dimension—the ability of each country to appeal to the populations of other countries and persuade them that one’s own country is more peace loving than its rival—do the incentives seem to work in favor of moderation and compromise. It is all too easy, then, to imagine China and the United States blundering into military conflict.

Brooks and Wohlforth’s assessment of hard-power relations may well be right. But the authors miss more significant relational issues. Drawing a balance sheet of hard-power resources held by China and the United States does not answer crucial questions about the most important potential sources of war. Power is contextual, so the implications of such a balance sheet will depend on the situations in which conflict arises. The United States can more easily deter a Chinese attack on its mainland or on its Australian or Japanese allies than it can a Chinese attempt to conquer Taiwan, which Beijing considers part of China.

Ultimately, the uncertainty created by rising Chinese power and ambiguous American power is more important than the balance of hard-power relations between the two states. If analysts don’t understand why, they should look back to July 1914. Experts from that era would have been wise to pay more attention to the dynamic uncertainty and the potential for unanticipated interactions inherent in the international system than to the relative economic or military capabilities of various countries. In 2023, the foreign policy community should also direct more attention to the potential for dangerous and unpredictable interactions resulting from changes in military technology and crisis dynamics rather than conduct an inventory of power resources.

Brooks and Wohlforth Reply

In “The Myth of Multipolarity,” we showed that if the term “polarity” is defined as it was by the scholars who invented it—namely, as the distribution of power resources that states can use to pursue their aims—the international system remains closer to unipolarity than to bipolarity or multipolarity. One country, the United States, is still far more powerful than even its closest competitors. It boasts the world’s strongest military and the world’s biggest economy. It is home to a vast proportion of the world’s leading technology firms. It dominates the world’s alliance systems. No other country, not even China, will be in the same league in the foreseeable future.

We labeled the current system “partial unipolarity” to emphasize that although Washington’s lead remains substantial, the power gap has narrowed from the “total unipolarity” that existed right after the Soviet Union’s demise. But this characterization of the world still earned objections from several notable scholars. In their responses to our piece, Joshua Shifrinson, Anne-Marie Slaughter, Bilahari Kausikan, and Robert Keohane take issue with our assessment of Washington’s power and what it means. They write that the world is no longer unipolar—or that if it is, this unipolarity is irrelevant.

But these authors fail to present compelling alternative definitions of multipolarity. They cannot prove that unipolarity is of little international consequence. They do not show that U.S. leadership is insignificant. And appearances notwithstanding, none of the responders ultimately contests our core claim: that the United States remains, far and away, the world’s most powerful country.

DOUBLE STANDARDS

How can this be, when Shifrinson flatly concludes that “unipolarity is no more”? The answer is that Shifrinson’s critique is largely semantic. He does not argue that other states have become true peers of the United States and indeed suggests they have not. Instead, he simply redefines unipolarity as a world “dominated by Washington—and by Washington alone.”

This definition is not unfamiliar. Analysts have a penchant for using implausibly high standards for judging U.S. power while using easy-peasy thresholds for other countries. Shifrinson, for example, says that if a state can “influence other leading countries’ calculations in peace and make a good showing against them in war,” it is a pole. But there has never been, and will never be, a country that can win against all others across all contingencies without much of a fight, just as there has never been, and will never be, a country that does not have to think about the potential influence of any other states when it makes foreign policy.

Consider, for example, the immediate post–Cold War years, when everyone agreed on the United States’ unprecedented preeminence. China and Russia still had what Shifrinson would describe as “good enough” technology to influence U.S. foreign policy choices. They would have been able to make a decent showing against the United States in a war had Washington been foolish enough to attack either of them. And they were hardly the only countries that challenged U.S. authority.

A quick glance at this magazine’s articles in the two decades after the Soviet collapse makes it abundantly clear that U.S. freedom of action was sometimes constrained and that Washington’s dominance was routinely contested by all kinds of unruly powers, including Afghanistan, Iran, Iraq, North Korea, and Serbia. These countries took steps such as developing nuclear weapons, funding terrorists, and staring down the United States in tense conflicts. Balky allies jumped ship when Washington wanted to move against Iraq, and various countries formed regional trade blocs that created tension with the U.S.-led global economic system. Leaders across Asia and Europe talked about multipolarity and established new “anti-hegemonic” initiatives. Using a definition of unipolarity essentially the same as Shifrinson’s, the political scientist Samuel Huntington wrote an article admonishing U.S. officials “to stop acting and talking as if this were a unipolar world.” That was in 1999.

For Shifrinson, the requisites of a “pole” are so low that a lot of states qualify. Ukraine has proved it can “influence other leading countries’ calculations in peace and make a good showing against them in war.” States such as Iran and North Korea have been able to meet these thresholds since the 1990s. France and the United Kingdom both qualified in the early part of the Cold War, and by the Cold War’s later years, China, Germany, and Japan did as well. But during the Cold War, there was a near-universal consensus that the world had just two poles: the Soviet Union and the United States. It would be revisionism to suggest that other countries occupy anywhere near the same position. In defining unipolarity out of existence, Shifrinson waved away bipolarity as well. By his lights, all systems are multipolar.

The problem with Shifrinson’s thesis—changing the standards for what counts as a pole depending on the country—is endemic to debates over U.S. power. At any given moment, observers are struck by the limits of Washington’s influence and the challenges the United States faces. They are rarely as taken with the more severe constraints on Washington’s competitors. To use a baseball analogy, analysts ask the United States to consistently hit home runs and fixate on the moments it cannot. Meanwhile, they admire other powers for their ability to bunt. It makes sense that policymakers, defense planners, and defense contractors would use this double standard as they argue for their preferred priorities. But it is less clear why academics would adopt it, too. These analytical flaws do not mean Shifrinson is wrong about the obstacles the United States faces today. Indeed, we agree with his succinct summary of today’s strategic constraints, and we share his view that they are tougher than the ones the United States faced in the 1990s and the following decade. We stressed that in the age of total unipolarity, China and Russia were unwilling to even minimally challenge the status quo, whereas in a time of partial unipolarity, they are prepared to test Washington. They can even succeed if they choose small, easy, and less consequential targets (as Russia did with Crimea, and China is doing in the South China Sea). But the revisionist challenges the United States faces now pale in comparison to those faced by the most powerful countries in multipolar and bipolar eras.

These constraints are readily apparent when considering the worst-case scenario for U.S. interests. If matters go very badly for the United States and its allies, and very well for revisionist actors, Russia could successfully conquer around a fifth of Ukraine and China might acquire Taiwan. As tragic and unwelcome as those developments would be, they would not truly transform China’s or Russia’s international positions. But worries about such portentous revisionism were routine in past systems, as during the Cold War, which, as our article explained, would have fundamentally changed the balance of power.

INTERNATIONAL AUTHORITY

Slaughter, Kausikan, and Keohane—unlike Shifrinson—do not attempt to contest our description of U.S. power. They all agree that by the standard metrics used to measure power resources, the United States remains in a class by itself and that it will be a long time before China could be a peer. Their arguments instead center on a different point: that our argument is, effectively, immaterial. The United States’ standing as the sole superpower, they write, does not really matter in a world beset by a wide variety of transnational problems. And although they agree that the United States remains the dominant global force, they assert that we overlook other important international actors.

Slaughter, for example, takes a particular interest in the European Union, which she views as another pole. She points to its U.S.-sized economy and its members’ powerful armed forces as evidence of its weight. And she argues that the EU has shown it is an essential global player.

We agree the EU is a major force on trade, global regulation, international norms, international development, and other issues. But it is no pole. As we wrote in these pages 21 years ago, Brussels could only become a pole if it developed “impressive military capabilities” and wielded “its latent collective power like a state.” To do so, it would have to create “an autonomous and unified defense and defense-industrial capacity” that would be “under the control of a statelike decision-making body with the authority to act quickly and decisively.” Such a body could “be purchased only at the price of a direct frontal assault on European nations’ core sovereignty.” Unsurprisingly, Brussels never created it.

Basic explanations of global politics can help analysts uncover critical insights.

In fact, the EU has a smaller pool of power resources today, relative to the United States, than it did in the first decade of this century. And as one of us (Brooks) wrote in International Security, the EU’s ability to act decisively in foreign policy is hamstrung by the continued independence and “strategic cacophony” of its members. They diverge in many important domains, such as threat perceptions, constraining coordinated action. Real poles have the potential to mobilize resources at all times to act in all areas, not just sometimes in some areas.

The other responders might disagree with our conclusion about the EU, given that they are dismissive of raw calculations of power and instead focus on influence. Kausikan in particular suggests that any state with global sway should count as a pole and that there are, accordingly, many of them. It is easy, after all, to find anecdotes featuring the United States not getting what it wants as a comparatively poor actor exerts substantial influence. This fact is why Kausikan says our analysis of U.S. strength vis-à-vis China and other states is “correct but beside the point” and insists that the international order is “indeed multipolar.”

But Kausikan, like Shifrinson, makes the case against unipolarity by defining it out of existence. If unipolarity means that the United States must “run the show” and polarity is defined by how countries “perceive their strategic choices and exercise their agency,” then it is hard to think of a system that is not multipolar. This approach creates the same problem that Shifrinson’s does: multipolarity becomes a constant, not a variable, and the shifting balance of power therefore cannot be used to explain change.

THE POWER OF POLES

Like Kausikan, Keohane seems to suggest that polarity is an unhelpful concept and that analysts would be better off not reckoning with the power resources of states. If so, we strongly disagree: polarity remains a critical tool for understanding international relations for all kinds of reasons. Analyzing poles may be a simple way to describe the world, but basic explanations of global politics can help analysts uncover critical insights. By isolating the effects of polarity, analysts can also better understand the significance of variables that have little to do with the balance of power. And by focusing on polarity, experts can track how international politics changes over time.

For our part, we have used the same standard to measure polarity for more than two decades: How much of a lead does the United States have in the military, economic, and technological realms? We focused on that gap because it reflects the core insight from scholars, most notably Kenneth Waltz, who popularized the idea of polarity: international politics works differently depending on the number of roughly comparable states at the top. For all its bluntness, this approach does help experts see some key distinctions about the world today compared with the world of 1945, 1985, and even 2000.

Most foreign-policy analysts and policymakers grant that polarity is important; they would not frequently discuss it and make claims about it if they believed otherwise. In her response, Slaughter even writes that polarity is a “key background condition for officials to consider as they formulate policy.” Nonetheless, Slaughter’s main problem with our article seems to be that it is about polarity. It is not hard to infer why. Her critique—like Kausikan’s and Keohane’s—suggests that we think other factors do not matter in explaining the world. But at no point did we assert that polarity is the master variable that explains everything, and we are fully aware that the study of polarity is no substitute for careful consideration of webs of interdependence and relationships. We certainly accept that international institutions, norms, ideas, the global economy, technology, and new forms of interdependence are shaping the world. We simply believe that a careful focus on the balance of power is valuable, as well.

So why do these three responses all interpret our article as making extravagant claims about polarity’s importance? The answer may lie in the tendency of some prominent realist scholars to assert that polarity is far more important, empirically, than other variables. In our view, that claim was wrong even in the mid-twentieth century when the concept was invented, and it is less true now. Kausikan stresses that middle and smaller powers can and often do play key roles in important events; we certainly agree. Smaller powers exert more sway today than they did in the past, especially compared with the era when large empires ruled much of the planet. Yet the fact that lesser powers matter more does not mean that the world is multipolar or that polarity no longer influences global politics.

AMERICA FIRST

There is a final reason why polarity is worth studying and why the endurance of American unipolarity is important. Although Keohane is right that polarity alone does not prevent major war, and although Slaughter is correct that transnational threats receive insufficient attention, interstate conflicts and transnational threats would be even scarier if the world were bipolar or multipolar—and if the United States were not its leader.

To an extent, analysts can be forgiven for forgetting these facts. Washington has been leveraging its massive power resources to provide leadership for so long that people have trouble thinking about what the world would look like without U.S. oversight. In our 2016 book, America Abroad: The United States’ Global Role in the Twenty-First Century, we carefully examined this counterfactual. The picture was ugly: more states had nuclear weapons, the risk of war between major powers was significantly higher, the prospect of international cooperation was much lower, and disruptions to the global economy were more frequent and more harmful. Russia’s war in Ukraine offers a small taste of what life under those circumstances might be like, and it is so dangerous and destabilizing that it is easy to underestimate how exceedingly rare wars of territorial conquest have become. Great-power war has been completely absent in the nearly 80-year period since World War II, during which Washington has pursued a global grand strategy.

The deployment of U.S. power is not the only reason for this relative peace, but it is an important one. If the United States were not using its immense power to shape the world, global stability would likely hang by even more tenuous tenterhooks than it does now. The fears and apprehensions Keohane identifies would be even more intense, all exacerbated by the presence of dozens more nuclear weapons states than exist today. A world without the United States at the top of the global power heap would also be less likely to attain the international cooperation needed to address important transnational threats such as climate change and migration. After all, threats alone are rarely enough to compel states to cooperate.

For those who want more concerted action on transnational problems, our article’s findings should therefore offer hope. As Keohane stressed in a 2012 article in these pages, “Leadership is indeed essential in order to promote cooperation, which is in turn necessary to solve global problems ranging from war to climate change.” Yet for a leading state to promote international cooperation, it must want such cooperation to occur. Although there are many reasons to be disappointed in U.S. efforts to tackle transnational challenges, there is every reason to think that Beijing would be doing much less as the world’s leader. If the world truly had shifted away from unipolarity, its problems would likely be much more acute than they are now.