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date: 16 August 2017

Unipolarity: The Shaky Foundation of a Fashionable Concept

Summary and Keywords

Since the Cold War’s end, academics and policy analysts alike have described the international system as unipolar. The term’s use appears well grounded. The United States possesses exceptional relative capabilities by historical standards, with capabilities—including control of the skies—that were unimaginable under British, Dutch, Spanish, and Portuguese hegemony. The system seems unipolar then when assessed using a common method for discerning polarity: counting the number of unusually powerful countries in the system. But the numerical case for U.S. preeminence is far easier to make than a logical argument for judging the number of poles in the system. Logic actually suffers considerably when analysts base their thinking about unipolarity on the common assumptions that (a) the Cold War-era international system was bipolar, (b) the current system is unipolar, (c) polarity is discernable from aggregate capabilities, and (d) polarity is detectable in interstate behavior.

Keywords: unipolarity, empirical international relations theory, Cold War, multipolar

Unipolarity: The Shaky Foundation of a Fashionable Concept

Since the Cold War’s end, academics and policy analysts alike have described the international system as unipolar. Indeed, “unipolarity is arguably the most popular concept analysts use to assess the U.S. position in the international system that emerged in the wake of the demise of the Soviet Union” (Brooks & Wohlforth, 2015/2016, p. 7). The term’s use appears well grounded. The United States possesses exceptional relative capabilities by historical standards, with capabilities—including control of the skies—that were unimaginable under British, Dutch, Spanish, and Portuguese hegemony (see Thompson, 2006). The system seems unipolar then when assessed using a common method for discerning polarity: counting the number of unusually powerful countries in the system (Rapkin, Thompson, & Christopherson, 1979, p. 263). But a numerical case for U.S. preeminence is far easier to make than a logical argument for judging the number of poles in the system (see Mansfield, 1993, pp. 108–110). Logic actually suffers considerably when analysts base their thinking about unipolarity on the common assumptions that (a) the Cold War-era international system was bipolar, (b) the current system is unipolar, (c) polarity is discernable from aggregate capabilities, and (d) polarity is detectable in interstate behavior.

Was the System Bipolar?

Analysts frequently take an intellectual shortcut when reasoning that the contemporary system is unipolar: They assume that its predecessor was bipolar. Given that the Soviet Union ceased to exist, and Russia is a weak replacement, the logic is “two minus one equals one.” All other things being equal, a bipolar system that loses a pole is unipolar (Mowle & Sacko, 2007, p. 18). That this logic affected analytical thinking at the end of the Cold War is apparent from the speed with which observers accepted the “new” international system as unipolar. The implicating logic is suspect, however, because the United States did not claim former Soviet capabilities, which means that these “lost” Soviet capabilities cannot count favorably for the United States in the revised numerator of the U.S.-to-global power ratio. What counts then in the numerator and denominator when expressing relative U.S. capabilities of the Cold War and post-Cold War system? The Cold War system was not bipolar, in fact, with certain calculating assumptions.

One common bipolarity assumption is that two countries must be strong enough together that no conceivable coalition of third countries could advantage one of the preponderant states. Kenneth Waltz (1993, p. 73) applies this standard when claiming that “with two great powers, balancing is done mainly by internal means. Allies have been useful and have therefore been wanted, but they were not essential in the security relations of the big two.” Yet, a military coalition that joined the United States with the Western European countries of NATO, the Eastern European countries of the Warsaw Pact, China, and Japan would have encircled the Soviet Union, and presented a formidable bulwark in global manpower, technology, and economic might to contain any Soviet threat. Even if Soviet survival was secure, such a coalition would have challenged Soviet claims to superpower status by limiting Soviet capability to project power in virtually any part of the world. Indeed, such a coalition would arguably have made the global system “multipolar,” not bipolar, for it would allow an alliance of non-superpowers to tip the balance toward, or away from, either dominant state.

That analysts accept this bipolarity assumption is curious, in any case, because analysts so frequently undermine it by stressing the role of crisis, instability, and adjustment under bipolarity (see Rosecrance, 1966, pp. 314–315) as when referencing the insecurity that the superpowers displayed from their perches of alleged preponderance. How can analysts argue that third countries could not threaten U.S. and Soviet preponderance while acknowledging that the two dominant powers competed widely and intensely? By fighting proxy wars, subverting governments, soliciting UN votes, spreading arms, and distributing aid, these states acted, by this accounting, as if the balance was highly sensitive to alliance building.

A seemingly less-demanding variant of the same assumption is that the two strongest countries jointly (but not singularly) possess at least half of relevant systemic capability, with each possessing at least a quarter (Rapkin et al., 1979, p. 269). In a sense, these dominant countries must claim a “controlling share” of global power. But the 50%- standard applies when a bipolar system amounts to a conspiracy of the strong against the weak, not when the dominant powers compete with each other. With such competition, this standard shifts control, by implication, to weaker states that supply the “swing votes” in the system. Two ostensibly “polar” states, each possessing 25% of systemic capability, can become stronger relative to each other by acquiring allies from among these weaker states.

The system can remain highly unstable, then, even when the superpowers together “control” much of the capability in the system. For instance, should the two coequals claim 80% of military assets within the system, the 20 percent of capability in play could give one power a 60–40 (that is, a 50%) capability advantage over its competitor. Although such an edge might seem inconsequential, all judgments in that regard are intuitive and probabilistic, not logical.1 Without a logical standard for determining what constitutes meaningful control of system capability, bipolarity can only be said confidently to exist (by a standard of predominance) when the two superpowers control all the capability in the system.

The logical challenges mount when recognizing that capability stems from many interdependent dimensions. Waltz (1979, p. 131) notes, in this respect, that states “use their combined capabilities in order to serve their interests” and that these capabilities “cannot be sectored and separately weighted.” He assumes then that these capabilities augment rather than complement one another, that is, that these capabilities are not useful at different times for different purposes. He also ignores potential tensions among the components stemming from their mutual dependence, as Waltz (1993) himself later recognized (and discussed at length). These critical tensions mattered far less to the United States than to the Soviet Union. Whereas U.S. leaders could draw upon a well-developed economy to produce state-of-the-art weapons, field a well-trained army, resupply forces, provide necessary logistical support, and acquire military resources without hurting the civilian sector, Soviet leaders, by contrast, had to contend with serious economic constraints. Ultimately, they had to rethink their global posture under the burden of maintaining a qualitatively and quantitatively competitive military force (Wohlforth, 1999). That a moribund economy would bring down the Soviet Union was little appreciated by international politics theorists at the time. Their focus was on overall superpower capabilities and their versatility, not the drain imposed by some capabilities on others. Even those who now argue that Soviet economic weakness allowed the United States (of the Reagan administration) to “win” the Cold War were far less confident in victory at the time and insisted that a principal danger from the Soviet Union was its unrelenting willingness to do whatever it took to defeat the West including starving the Soviet civilian sector. The neglect of the economic in strategic assessments rightly prompted Wagner (1993, p. 88), for one, to ask, “how small did the Soviet economy have to become before the structure of the international system could be said to have changed?”

Is the System Now Unipolar?

Similar issues arise from the contemporary literature on unipolarity. Krauthammer introduced the term (in the immediate aftermath of the first Gulf War) when pronouncing that “there is but one first-rate power and no prospect in the immediate future of any power to rival it.” In his words, the United States “is the only country with the military, diplomatic, political and economic assets to be a decisive player in any conflict in whatever part of the world it chooses to involve itself” (1990/1991, p. 24). Academic works offer equally broad definitions. Walt (2011, p. 105, 108), for instance, defines a unipolar system as “one in which a single state controls a disproportionate share of the politically relevant resources of the system.” Consequently, “it enjoys greater freedom of action because it does not have to worry about direct opposition from any country possessing roughly equal capabilities.”2 These broad definitions tellingly invoke ambiguous terms—“first-rate power,” “decisive player,” and “disproportionate share”—that affect how unipolarity is understood and whether it is judged relevant to a system at a given time.3

Analysts can avoid vague definitions that trade one amorphous term for another by invoking explicit standards. Indeed, analysts do attempt precision, in defining unipolarity, when adopting mathematical reasoning of the sort that influences thinking about bipolarity. But precision again imposes costs when standards lack logical support.

Unipolarity based on a 50% standard—a single state controlling at least half of the power of all major contenders—is one benchmark in the literature (see, e.g., Thompson, 2006, p. 12). As before, the logical challenge is obtaining a useful denominator for measuring relative U.S. capabilities, worsened now that the focus is on third country capabilities that so confounded Cold War-era analyses. Given the absence of an accepted baseline (denominator) for comparison with U.S. capabilities, definitions of unipolarity are bound to be problematic. How can you say with certainty that a state controls a majority of power when uncertainty exists over the composition of the comparison group?

The logical issues are by no means restricted to the function denominator; they afflict the numerator as well. When Robert Pape (2005, pp. 11–12) claims that unipolarity exists when a state is sufficiently strong “that no other single state is powerful enough to balance against it,” he suggests that unipolarity exists when a state controls a mere “plurality of power.” A simple plurality does a country little good, however, when other states can form offsetting coalitions to challenge the dominant state. Pape only compounds the intellectual problems when he pairs his numerator with a rickety denominator that appears to stiffen the requirements for unipolarity. He observes accordingly that the offsetting coalition in such a system “would have to include most or possibly even all of the lesser major powers” (Pape, 2005, p. 11) and equates unipolarity, then, with being more powerful than the top half of second-ranked powers. In doing so, he now appears to raise the bar too high—given the potential capabilities of “smaller” coalitions that include, say, China and Russia—if he sticks to his judgment that the current system is unipolar. This is the effect, too, when Pape distinguishes a unipolar from a multipolar system in concluding that there is “at least one state that can mount a reasonable defense, at least for a time, even against the multipolar leader” (Pape, 2005, p. 12). Whether such a defense is currently possible depends on exactly what is being defended (when and how), whether defense is an all-or-nothing proposition, and how much the challenger values the stakes. It would certainly be difficult for the United States to occupy China, for instance, “for a time” that was politically or militarily significant. For that matter, the United States was hard pressed to provide military forces on the heels of the Iraq war (in the first years of the Obama administration) to prevent further Taliban gains and “reverse its momentum” in Afghanistan.

As some analysts imply, at least, unipolarity defies an exact standard. For that reason, the United States could achieve predominance with less capability than it currently possesses. William Wohlforth (1999, p. 29) observes accordingly that the obviousness of U.S. preponderance frees the United States from having to maintain an excessively large force to reduce adversary uncertainty about U.S. capabilities. In turn, countries that unite to challenge the U.S. position might find that their seemingly abundant aggregate capabilities are inadequate for the task. Stephen Brooks and William Wohlforth (2005, pp. 84–85) observe, on this point, that balancing is not a “frictionless, costless activity.” States must sacrifice some capability when struggling to negotiate rules and responsibilities and overcome distrust (including fears of defection) within a coalition. A militarily resurgent Japan or Germany, for example, will invite trepidation in neighboring states given the unpleasant historical memories that rearmament will trigger. Assuaging mutual suspicions through some inefficient manner of armament invites cost as does guarding against duplicity in alliance formation. Inefficiencies and performance shortfalls also occur through free-riding impulses that lead allies to shirk, otherwise place their own interests first, and thereby pass burdens to their military partners. Thus, Barry Posen (2011, pp. 323–324) is correct to ask whether the unipole must “merely need to be sufficiently capable that any opposing coalition would need to include so many independent actors, and operate so efficiently, that it would prove to be the most effective military alliance in modern history?”

These are arguments for assuming, however, that unipolarity exists at some level below a designated baseline, not for disclosing the actual baseline. The lack of theoretical direction for determining this cut point is all the more glaring when recognizing that “friction” encumbers the weak and the strong. Power is lost through “friction” when predominant states employ capabilities that are deficient or inappropriate under the circumstances (e.g., irregular war), struggle to convince allies to share a military burden, perform at less than full strength under the weight of multiple commitments, and accept political restrictions in the conduct of military operations. In consequence, the dominant power requires capability at (net) levels higher than the baseline to exert meaningful influence within the system.

Of course, scholars might surmount the intellectual challenge by changing the terms of debate. With that intent, Nuno Monteiro defines unipolarity as a system of only one great power where a great power possesses “robust capabilities in all the relevant elements of power,” can defend itself against aggression, and possesses “the ability to engage unaided in sustained politico-military operations in at least one other relevant region of the globe beyond its own on a level similar to the most powerful state in the system” (Monteiro, 2014, p. 44). Monteiro thereby adds requirements to an already shaky definitional approach centered on aggregate capabilities. Monteiro invites conceptual problems, then, and reasons to question his definition. Why should a theory of the global system rest on power projection capabilities in a single region when a preponderant state might confront simultaneous and continuous global challenges in various “relevant” regions around the world? Indeed, the Obama administration’s ostensible Asia pivot, to address challenges from China, was encumbered by the continuing demand for U.S. forces in the Middle East and South Asia (Afghanistan).4 Moreover, what does “projecting power” require in practice? It is one thing for the United States to engage in operations for which U.S. conventional capabilities are well suited and quite another to try to quell violence in countries in which governance is contested or absent.

Commendably, Monteiro recognizes that nuclear weapons, in the hands of major powers, change the force equation. Omitting nuclear weapons from the formulation was a glaring omission in Waltz’s seminal bipolar analysis, as he later acknowledged (Waltz, 1993). But exactly how do these weapons weigh into the assessment? Monteiro, for one, assumes wrongly that these weapons immunize possessors from conventional attack. Many U.S. deterrence theorists assumed, to the contrary, that the neutralizing effect of the joint possession of nuclear weapons freed the United States and Soviet Union to compete at lower levels of conflict. Indeed, U.S. policy hawks feared that the Soviets might launch a “limited” nuclear attack against the United States because its threat to retaliate lacked credibility given the likely magnitude of the Soviet response. Monteiro fails, in general, to assess the requisites of nuclear security. He makes much of overwhelming U.S. nuclear superiority yet suggests elsewhere that it hardly matters, for example, when he maintains that the U.S. nuclear position is sufficiently fragile to require safeguarding (with resources acquired through ongoing economic growth) or that fear of retaliation deters the United States (the unipole) from attacking any nuclear-armed state.

In sum, similar challenges afflict judgments about system unipolarity and bipolarity. All definitions, implicit or otherwise, suppose that the “polar countries” stand, somehow, above the rest. By these definitions, unipolar analyses present a one-dimensional problem: At what point along a continuum does the predominant state control sufficient systemic capability for analysts to conclude that a system is unipolar? Bipolar analyses present a two-dimensional problem: How much capability must the two powers control jointly and singularly to make for a bipolar system? But these questions reduce to the same basic question, “how much capability does a country require to establish its polar position?”

As Figure 1 demonstrates, neither question is easier to answer, then, than the other. Just as it is not apparent that the two distributions are inherently less unipolar in Figure 1a, whether the predominant state claims 40 or 80% of systemic capability, the distributions are not fundamentally more or less bipolar in Figure 1b, regardless of how shares are distributed. That is, the analytical problem persists whether the shares are divided evenly or unevenly among the two dominant states or between them and other states, whether the predominant states exert minority or majority control in the system.

Unipolarity: The Shaky Foundation of a Fashionable ConceptClick to view larger

Figure 1. Hypothetical Power Distributions Suggesting Unipolarity and Bipolarity.

Thus, if bipolarity is the more problematic of the two concepts, it is only because bipolarity invites additional logical questions. Specifically, if the superpower balance can be overturned through alliances with other states, what makes the primary powers “super?” Conversely, if the balance cannot be overturned, what make the bipolar system “polar?”

Is Polarity Discernable From Aggregate Capability?

No amount of pure mathematical reasoning is sufficient, in fact, to conclude that the Cold War-era system was bipolar or that the current international system is unipolar. Even controlling most—or, almost all—of the “power” in the system is not advantageous when a “majority stake” is insufficient to accomplish narrowly defined military objectives.

What works, in fact, against one country in battle will not necessarily work against another. Illustrating this are British and German capabilities at the end of the 19th century, which appear approximately equal though Britain “ruled the waves” and could control access to and from the sea and project maritime power in various parts of the world. In turn, Russia appears many times stronger than Japan in roughly the same period—on the eve of a war between the two countries that Japan won decisively due, in part, to its ability to transport forces more quickly to the conflict zone (Moul, 2003, pp. 477, 479–480). For that matter, despite apparent “bipolarity,” a U.S.-Soviet conventional war would have amounted to a battle of (rough) equals only in Europe. The United States was actually the preponderant state within the global system in key respects (e.g., in power projection capability) throughout the Cold War period and the Soviet Union was more of a regional power, at least in terms of conventional capabilities. As Wagner (1993, p. 79) observes, “the distinctive feature of the postwar distribution of power . . . was not that two states were more powerful than the others . . . but that one state, the Soviet Union, occupied in peacetime a position of near-dominance on the Eurasian continent.”

Although all power rankings assume implicitly that relative power conforms to a transitive ordering principle, the outcome of conflict is often specific to the match-up—and then the terms of competition. This is obvious in sporting events when the underdog triumphs because it can exploit the “stronger” team’s vulnerabilities or benefit from game conditions such as weather. It is clear as well in military conflicts. A U.S. effort to halt a Chinese amphibious assault on Taiwan will play out differently than a war fought to halt a North Korean land invasion of South Korea (not to mention U.S. wars against assorted others in Central Asia, Africa, the Middle East, or Europe). Outcomes will vary, as well, with the issues, including territories, at stake. With its huge manpower advantages and land army, China makes for a formidable opponent in any battle fought in and around the Chinese mainland but lacks air and naval power to extend its global reach, and shows few signs of overcoming these deficiencies. U.S. leaders have well appreciated the liabilities of tackling adversaries near or around their home turf. Despite retrospective analyses that suggest that the United States acted out of fear of Soviet reactions during the Cold War but can now act with “greater freedom of action” (Walt, 2011, p. 108), the United States has always acted out of fear of provoking “lesser” powers. Both the Johnson and Nixon administrations observed restraints in the Vietnam War so as not to provoke direct Chinese intervention; in turn, the Bush and Obama administrations observed restraints toward Iran—for example, by forgoing attacks on its nuclear facilities—to avoid an Iranian response that could compromise the U.S. position elsewhere in the Middle East.

The challenges of evaluating the usefulness of material capabilities bedeviled assessments of the Cold War period and remained in the decades that followed. It was certainly easier for analysts to conduct net assessments of superpower capability than to judge the United States or Soviet ability to shape outcomes on various fronts. Yet, force-on-force capabilities were subjects of constant—indeed, inevitable—debate. Just as analysts asked whether the Soviets had achieved conventional force supremacy in Europe, arms-control analysts debated the meaning of nuclear “parity,” and whether “inequalities” in U.S. and Soviet force deployments gave the Soviets a nuclear edge. It is unsurprising, then, that some analysts look back now at the Cold War period as actually one of U.S. hegemony, or that the “numerical” basis for this judgment is not fully explicated, and begs for scrutiny. Much is left unsettled, for instance, when Christopher Layne (2006a, p. 149) suggests that amassed Soviet conventional capabilities were insufficient to challenge the dominant U.S. position in Europe while arguing that China and India are each bringing the current international system closer to multipolarity.

The fact is that, for even the United States—the strongest of military powers—the impediments to the effective use of military force are considerable. These impediments appear obvious in the wake of recent U.S. wars in Iraq and Afghanistan and the U.S. effort to balance their competing demands. Yet, these wars only made obvious the preexisting impediments to all predominant states in their exercise of power. These impediments are as follows.

First, a predominant state—with its global concerns and commitments—cannot invest fully in conflicts when the stakes (for that state) are small (Art, 1980, p. 25). Engaging in “small wars” can distract the United States from more critical global responsibilities and commitments. Even for minor contingencies, aggregate statistics tend to exaggerate the divisibility of U.S. forces for simultaneous (or consecutive) operations. Troop strength, for instance, is a deceptive figure given rotation demands and noncombat roles that have most troops supporting the work of others. Actions on one front could have consequences on others. Escalating the fighting could compromise the U.S. political and normative standing, at home and abroad, weakening the capability of U.S. leaders to accomplish their goals in other parts of the world. Thus, a weaker party might control the pace and severity of fighting to capitalize on constraints that inhibit the “stronger” party from engaging fully, and prolong a war then to secure a more favorable negotiated outcome (Mack, 1975; Pillar, 1983; Wagner, 2000).

Second, capability that is appropriate under some conditions is inappropriate under others. Because powerful states must worry about major threats (and major rivals) and must craft their military capabilities and doctrines accordingly, the military capabilities that the United States has available to address other threats are often not up to the task. Indeed, lead powers have traditionally lacked a significant capability to “project their influence inland” and possessed capabilities that were intended primarily to control the commons, in support of “constrained systemic leadership” (Thompson, 2006, pp. 11–12). Lesser adversaries could potentially offset U.S. capabilities. U.S. adversaries of the Cold War and post-Cold War periods frequently countered U.S. strengths with guerrilla style hit-and-run tactics; low-profile platforms; mobile weapons; and explosive devices that are easily manufactured, planted, hidden, and activated.

Third, U.S. capability is exhaustible. The war in Iraq sapped U.S. equipment and manpower reserves, strained procurement and maintenance budgets, and produced military morale problems and manpower shortages. Exhaustion affects the military indirectly, too, by undermining its base in popular support. The conventional wisdom in public opinion research is that war support declines nonlinearly with mounting casualties (Mueller, 1971). Although these claims remain controversial, counterclaims that war support is bolstered by beliefs about a war’s likely success (Gelpi, Feaver, & Reifler, 2005) nevertheless provide a backhanded acknowledgment that the U.S. government must convince the public that a war is worth fighting and progressing as hoped.

An implication is, then, that even the United States—with its unprecedented expeditionary power—is poorly positioned for sustained military intervention abroad, except under favorable conditions, and will have difficulty imposing its will on a creative and determined opponent that can extend a conflict for the military or political returns. Indeed, the United States will find itself challenged militarily whenever serving U.S. goals depends upon the choices made by allies or adversaries (Sullivan, 2007). The success rate of the “more powerful state” in 20th-century conflicts is considerably lower than crude capability aggregates imply (Arreguín-Toft, 2005, p. 4; Lyall & Wilson, 2009, p. 69; Sullivan, 2007, pp. 502–503, 505). The U.S. wars in Iraq and Afghanistan suggest that the challenges only increase with the physical occupation of a country and the need (or urge) to reshape and build local political, economic, or military institutions. The complications multiply further when the United States is drawn into ethnic or religious fighting; when porous borders allow hostile neighboring states or expatriate populations to house, arm, and otherwise support opposition groups; and when (venal or partisan) government leaders abroad resist hard choices and economic or political reforms necessary for realizing U.S. military objectives. Thus, the U.S. wars in Vietnam, Iraq, and Afghanistan are not anomalies. When Walt (2011, p. 107) asserts, then, that “America’s daunting capabilities are a defining feature of the contemporary international landscape,” notwithstanding the “debacle in Iraq,” he misses the point that Iraq is a critical test case that trumpets the limits of U.S. capability.

Certainly, a large global capability share—or large amount of capability—is likely associated with an ability to accomplish military objectives on a global scale. But this, again, is a probabilistic judgment, not a logical inference. Analysts must stake their claims, instead, by linking capabilities carefully with their purported effects. Absent such reasoning, it is too easy to yield to temptation and accept the global system as unipolar and to exaggerate the capability of the preeminent state. Conversely, it is too tempting to pronounce the end of unipolarity when the unipole fails to live up to some inflated standard of capability, some dimensions of unipole capability experience relative decline, or trends move against the preeminent state. It is just such thinking that led Pape (2009, p. 21) to surmise, “(i)f present trends continue, we will look back at the Bush administration years as the death knell for American hegemony.” To say that the “unipolar moment” will soon pass, or has passed, is to beg the question, “did it exist in the first place?”

Is Polarity Detectable From Behavior?

Given the challenges of aggregate capability assessment, analysts often focus their definitional efforts on the nature and intensity of behavior within the international system. Cold War-era analysts concentrated their attention on relations between the superpowers (and within the two primary alliance systems); in turn, post-Cold War analysts have focused their attention on U.S. relations with second-order powers. Such a behavioral emphasis is necessary, by definition: behavior is organized around one or more primary powers that serve as pivotal objects of attraction and repulsion within a “polar” system. Indeed, the behavioral explanatory power of a specific capability distribution is critical for answering the question, “how much is enough capability?” But attention to behavior carries a significant risk of tautological thinking. A circularity in logic occurs when behavior is confused with the distribution of capability, or when any variety of behaviors can validate—yet, never falsify—prevailing assumptions about the capability distribution.

To a considerable extent, historical thinking about the global power distribution reflects the exceptional material attributes and (nonmaterial) behavioral characteristics of particular countries. The latter includes their participation in the rituals and activities that are associated with Great Power status, and their acceptance, as “Great Powers,” by other states.5 Indeed, perceptions of power derive in large part from behavior that means, in essence, that a state is a “Great Power” when it acts like one. As Jack Levy (1985, p. 62, fn. 19) observes, these states are widely recognized as “a group distinct from other states, and in many respects more important for international politics.” These states pursue broadly defined interests through a variety of means, maintain intense and frequent involvement in international politics, and attend to its “symbolic” dimensions.

The effects of behavior on perceptions of relative power are important because even “material” attributes (capability distributions) of the global system owed to the promoting and upholding of understandings of what to count and exclude. Offshore contenders were permitted to accumulate power when it did not threaten the land balance in Europe allowing Britain to maintain the lead position globally for centuries (Levy, 1985, p. 48). European relations of the 19th century actually deferred to elaborate sets of rules that helped preserve the peace while also permitting wholesale territorial expansion and pursuit of commercial interests outside of Europe (Finnemore, 2003). The result was a Concert that reflected the assumed distribution of regional power and affected the power distribution by holding states to certain standards.

Observed behavior continued to inform judgments about the global distribution of power, causing Cold War-era analysts to confuse bipolarity with polarization (Wagner, 1993, pp. 81–82; Waltz, 1964). Lost in their analysis was a critical difference: Bipolarity pertains to a concentration of power in two members while polarization relates to conflict exchanged between opposing groups in a system. Ignoring this difference, analysts often gauged the polarity of the Cold War-era system, then, by deferring to critical behavioral markers. These included the intensity of conflict between NATO and Warsaw Pact countries, degrees of intra-alliance cooperation, and the ferocity of superpower efforts to recruit nonaligned states and undermine aligned opponents in various parts of the world. The practice of discerning structure from behavior meant that analysts assumed that the structure changed with levels of international conflict and cooperation, even absent palpable shifts in the global power configuration.

In the prevailing analysis, then, system polarity tracked changes in U.S.-Soviet behavior. Consequently, the “tight” bipolar system of the 1950s stands in contrast with the “loose” bipolar system of the 1960s (when, for instance, France removed itself from the NATO command). Yet a discerning study of behavior arguably yields a different conclusion. After all, in the early 1960s, the United States reinforced its conventional force commitment to Europe (via a flexible response strategy) and, by the end of the decade, the Soviet Union had achieved rough equivalence with the United States in intercontinental nuclear weaponry. Indeed, bipolarity was often confused with “détente,” which was seen to ratify U.S.-Soviet equality (on this, see Rosecrance, 1966, p. 316). In turn, hawkish U.S. analysts took the intensifying tension in the years thereafter to indicate growing Soviet assertiveness stemming from relative Soviet military gains.

Ironically, a behavior emphasis could have yielded very different conclusions about basic system structure. Whereas the assumed symmetry of Cold War-era superpower behavior reinforced thinking that the global system was bipolar, an apparent asymmetry arguably revealed a distinct Soviet disadvantage, and weakness. The United States forged alliances in Western Europe by capitalizing on regional fears of a Soviet land threat and on shared economic interests that required regional and transatlantic cooperation. In contrast, the Soviet Union dominated Eastern Europe by supporting a network of repressive regimes and intervening occasionally to suppress rebellion.

Again, in the post-Cold war period, views of polarity—now, unipolarity—draw from assumed behavior patterns. The consequences, in illogical argumentation, permeate contemporary writings on U.S. hegemony, U.S. unilateralism, and “balancing” efforts by U.S. rivals.

First, analysts conflate capability and behavior in efforts to reconcile unipolarity with hegemony. The concept of “unipolarity” requires attention to the material capabilities of the primary power (and its behavior). In contrast, “hegemony” pertains to the nature of control—benign or malevolent—exercised by the primary power.6 A problem occurs, then, when analysts support their “polarity” assumptions by uncritically accepting evidence of “hegemonic behavior.” This failing is apparent when Layne (1993, p. 34) suggests that the United States has broadly and consistently acted to uphold its prevailing postwar global position and to deflect challenges from other states through a “strategy of preponderance.” Why must the United States reinforce its global position when the dominant state needs other states “less and thus will worry less about possible defection or defeat?” (Walt, 2011, p. 113). For that matter, why would states challenge the U.S. position to necessitate hegemonic behavior? As Brooks and Wohlforth (2002, p. 25) acknowledge, for example, challenging the United States involves forgoing benefits of association, not just accepting costs of confrontation.

Second, analysts embrace faulty logic when confusing a unipolar distribution with U.S. unilateralism, that is, when conflating unlimited U.S. power with the United States acting as if its power was unlimited. The confusion results when U.S. behavior rather than U.S. capability is the focus in the literature. Behavior is clearly central when the United States is alleged to use various carrots and sticks to maintain U.S. preeminence, promote U.S. interests, and “press [U.S.] preferences and values on others” (Layne, 1993, pp. 33–39, 46). Accordingly, much of the early unipolarity literature focused on instances of assertively self-interested U.S. behavior, as occurred when the United States shunned arms-control treaties, circumvented the UN Security Council when going to war, exempted the United States from the authority of international institutions (including the International Court of Justice and International Criminal Court) and conventions (such as the Kyoto Protocol), stood against the majority in the crafting of new agreements (including the verification measures for the Biological Weapons Convention), pushed drug and terrorism policies that shifted a sizable burden onto other states, employed the World Bank and International Monetary Fund to open economies to U.S. penetration, and generally ignored the preferences of U.S. allies.7 That the United States acted as expected served only to validate prior assumptions about overwhelming U.S. power.

Third, analysts invite illogic when viewing unipolarity in light of the balancing behavior of non-predominant states, and read resistance to the United States loosely, then, to measure relative U.S. power. By this accounting, the United States was sufficiently strong to provoke a response from other states and deter their hard-balancing efforts but sufficiently weak to tempt U.S. opponents to pursue the strategies of “soft-balancing” (to constrain U.S. power) or “pre-balancing” (to set the stage for hard balancing).8 Thus, whether the United States was strong or weak by this standard is unclear.9 It is reasonable to ask, for instance, whether the United States possesses formidable capabilities if U.S. rivals are aided, as is typically supposed, by these rudimentary (half-hearted) balancing efforts. Ironically, “soft-balancing” behavior—the supposed recourse of states seeking to avoid the risks of hard balancing (Pape, 2005, pp. 9–10)—actually reinforces U.S. political primacy in fundamental respects.

Given what U.S. challengers except and accept, their responses to unilateralist U.S. behavior arguably ratify an order that is based on U.S. global military engagement. States have challenged specific post-Cold War U.S. policies though not to promote themselves or some other power to the role of global policeman: “(o)ther great powers often resent America’s leadership, but their preference is for the United States to lead because they trust the United States more than they trust each other” (Art, 1998/1999, p. 82). NATO’s more capable members have actually raised the ire of the United States, not by challenging U.S. dominance, but by failing to maintain military preparedness and power projection capabilities to contribute to U.S-led operations abroad (specifically, in Afghanistan). In other respects, these countries have supported U.S. actions to reap benefits from coordination. Brooks and Wohlforth (2005, p. 84) observe, for instance, that foreign policymakers “have explicitly reoriented their strategic priorities to emphasize regional security issues such as terrorism and weapons proliferation on which they tend to have roughly similar preferences to those of the United States.” All such behavior actually speaks not to confrontation and balancing but to deference to U.S. capability to achieve shared goals.10

The bottom line is this: Behavior of various kinds and intensities is allowed to validate assumptions about the capability distribution, or else behavior is attributed circularly to a power distribution that, itself, is inferred from systemic patterns of behavior. A focus on hegemony, unilateralism, or balancing—without first resolving the key question of what constitutes unipolarity—is, at best, a distraction. At worst, it provides a false sense of the properties of the international system by exaggerating features of the current international system and contradicting the very assumptions that analysts make when they focus, instead, on relative capability.

The Concept of Unipolarity: Where Do We Go From Here?

Whether unipolarity usefully explains and predicts behavior in the international system depends on whether thinking about unipolarity is tied to behavioral consequences and linked more generally to conceptions of bipolarity and multipolarity. A fundamental rethinking of “polarity” is therefore required if unipolarity is to serve a useful function in theory and practice.

The rethinking should acknowledge that, as a theoretical concept, polarity draws its meaning from theory surrounding the term. As Stinchcombe (1968, p. 40) notes, “it is quite useless to discuss [these] concepts without reference to substantive theory about what goes on in the world, about what causes what.”11 The definitions of these concepts remain “in a constant state of flux as long as the causal theories are still in the process of development.” When analysts assert that “polarity is a theoretical concept”—to quote Ikenberry, Mastanduno, and Wohlforth (2011, p. 6) in the introduction to their edited volume—they must therefore concede the implications that follow. The first of these is that the concept of “polarity” has no meaning apart from the international behavior and causal logic that is associated with a given capability distribution.

Scholars only appear, then, to adopt a reasonable strategy in first settling the issue of whether the current distribution of capability is unipolar before addressing the distribution’s behavioral implications. But the questions of “how much is enough capability to make a dominant state a pole?” and “what consequences follow from the distribution?” are not open to sequential responses. They are effectively parts of the same question: Capabilities require evaluation in light of their consequences. The second of these implications, following from the first, is that “unipolarity” is inextricably tied, in its meaning, to the concepts of “bipolarity” and “multipolarity.” Scholars tend to focus on unipolarity as a distinctive system without grounding its behavioral properties in principles that explain the behavior of all polar systems.

To be sure, Ikenberry and colleagues (2011, p. 3) ask “to what extent—and how—does this distribution of capability matter for patterns of international politics?” The problem is the timing of the question—exactly when it is posed in the research agenda. Scholars should not settle their definitions first and then look for potential behavioral applications.12 Instead, they must tie their conceptual definitions of unipolarity to theoretical arguments about how, when, and why the capability distribution explains international behavior. Unfortunately, the result of ignoring theory-building in concept development is that scholars gravitate toward empirical observables: Their conceptual definitions are less about theory and more about the palpable—but arguably tangential or irrelevant—features of the contemporary international system.

At one level, it seems reasonable to proceed by settling the meaning of unipolarity before assessing its behavioral implications. Why not start where the light is brightest? In other words, why not accept the “obvious” fact of a concentrated post-Cold War capability distribution and move next to exploring its empirical implications? This research strategy is problematic, however, because it settles too easily for a conception of unipolarity that draws from common usage. Scholars fall back on ad hoc logic, in judging the capability distribution, and assume mistakenly that capability is measurable in crude aggregates that, in the U.S. case, actually overstate the unipole’s capabilities. The favorable imbalance in material resources does not translate necessarily into U.S. influence: All applications of U.S. capability invite challenges, overcommitment, and exhaustion (as previously discussed). The problems in such thinking emerge even when scholars assess the concept’s measurement properties. Ikenberry and colleagues (2011, p. 6) illustrate when they assume that effects of unipolarity will vary with its strength: “(t)he more unambiguously the poles in a real international system pass the threshold [“value of the distribution of capability”], the more confident analysts can be that the properties attributed to a given system structure in theory will obtain in practice.” It makes little sense for scholars to talk about unipolarity as a continuous variable without first ascertaining the properties of the system, that is, determining what unipolarity explains.

Analysts must recognize, then, that the theoretical question, “what is polarity?” logically precedes “what is unipolarity?”13 Placing the polarity question, first, redirects inquiry usefully to systemic characteristics and their effects. Granting polarity primacy offers an additional practical advantage: It pushes analysts to recognize that, in assessing “unipolarity,” they must stress polarity principles over principles that only govern that one specific structure. In developing their theories, analysis should follow certain guidelines.

First, polarity theorists must recognize that capability is not an undifferentiated mass and is a useful basis for sound theory only when tied to specific purposes. After all, even in a unipolar system, the strengths and weaknesses of a predominant state allow it to accomplish some goals more easily than others (and some goals, only at the expense of others). The strongest argument that the current system is unipolar rests, not on overwhelming U.S. power, but on the exclusive U.S. capability to perform tasks that critically affect the stability of the international system.

Historically, lead powers have not “sought control of European affairs,” generally lacked a significant capability to “project their influence inland,” and possessed capabilities that were intended primarily to control the commons, in support of “constrained systemic leadership” (Thompson, 2006, pp. 11–12). What these states possessed, then, was an ability to “control the commons”—the oceans (and now the skies)—for the trafficking of goods and personnel, both civilian and military. Indeed, the United States alone possesses the robust capability required to control the commons. The United States can deter and deflect major challenges to the global military status quo by bringing massive firepower to bear, in short order, around the world. The United States can protect against any, and all, conventional attacks on the U.S. homeland, act to prevent a destabilizing Eurasian war, help safeguard the sovereignty of Taiwan or South Korea, and maintain open access to Gulf oil supplies (see Art, 1998/1999). It can also support multilateral combat or peace operations: toward that end, it can provide logistic support, establish air superiority over the combat zone, and command the seas to and from hostile territory. This is a significant—actually, unprecedented—capability: The United States possesses “more useful military potential for a hegemonic foreign policy than any other offshore power has ever had” (Posen, 2003, p. 9).

Accordingly, theorists must ask, “which capabilities are essential to polar status and which are superfluous?” The answer will not come from any amount of abstract, mathematical, capability-centered logic; it will come, instead, when theorists tie capability—in its various configurations—to patterns of opposition and support within the international system. For realists, their shared attention to the “security dilemma”—the supposition that states act to offset the threat inherent in the power of others—makes it the logical starting point for theorizing about “systemic behavior under polarity.” A fruitful by-product of such basic questioning is that unipolarity will be seen in a new light.14 These probes could well spark a recognition that (a) the power of the predominant state is more robust than is generally assumed, and (b) the predominant state lacks the capability, nevertheless, to threaten others in a manner that necessitates balancing behavior.

Second, scholars who study unipolar, bipolar, or multipolar systems must understand that, above all else, they are “polarity” theorists. Although “polarity offers a stunningly bold way of simplifying the horrendous day-to-day complexities of world politics” (Buzan, 2004, pp. 40–41), therein lies the danger if the polar characteristics attributed to a system reduce to a grab bag of features unique to a given era.15 The central issue for analysis is not how unipolarity, bipolarity, or multipolarity work individually, that is, what properties make each of these systems distinct; instead, it is how theory might account both for the similar and dissimilar behavioral properties of systems that differ, first and foremost, in their distribution of power.

The danger of ad hoc theory about specific polar systems is the tendency to focus on properties that are particular to a given system. Walt (2011, p. 105) asks the right question (in presenting his own set of arguments): “which predictions reflect purely structural features (that is, the unipolar distribution of power) and would be valid no matter which state was the unipole [or who was its leader]?” A bias toward particularity could take various forms. For example, theorists might design theories around superfluous or tangential behavior, not regularities and continuities in aggregate behavior tied explicitly to a polarity theory. An emphasis, instead, on building polarity theory could inspire a useful recognition that (a) what states do not do is as important as what they do, and (b) cooperation can prevail over conflict within a system even when its concentration of capability increases.

Third, theorists must accept that an international system, defined around its polar characteristics, has variable boundaries. Systems theorists have long recognized that (e.g., regional) subsystems are connected in varying degrees, at varying times, to the “international system”—and, thus, that these subsystems might remain dominant under normal conditions. In consequence, a predominant state, even in a unipolar system, might sometimes exercise limited control over agenda setting and issue resolution; and the system, itself, might exhibit different behavioral properties depending on the matter at hand. A potential reward for recognizing that the international system exhibits changing limits might come through a recognition that (a) the polar structure of an international system can accommodate behavior that appears to contravene the principles governing the system, and (b) ill-defined systemic boundaries create unanticipated (probabilistic) outcomes that need not undercut the workings of a polar system.

Fourth, polarity theorists can continue to attribute behavioral consequences to the exceptional assets (capabilities) of key states within a system. In this, analysts can draw from the realist assumption that capabilities (and their distribution) shape the cost-benefit calculations of states as they evaluate threats, seize opportunities, and engage in various proactive or self-protective behaviors.16 Toward that end, analysts can consider the effects of capabilities on operant levels of uncertainty and attend to stability, peacefulness, alliance flexibility or “tightness,” and even balancing and bandwagoning—behavioral characterizations that draw from realist theorizing.17 As Buzan (2004, pp. 31–32) observes, thinking about polarity is embedded firmly in the realist tradition in placing the analytical focus on the material capabilities of states and the predominance of great powers.18 Indeed, the risk of inattention to capability is a tautological reasoning that elevates states to polar status by merit of their exceptional behavior within the system and a “theory” in consequence that lacks explanatory or predictive power. As great a danger in focusing principally on behavior is that capability will be assumed to matter in the system only when perceived (“credible” power) or accepted (“legitimate” power) as such.

To start, in fact, by focusing on behavior risks a self-fulfilling prophesy that has theorists focusing on everything but the factor—the material capabilities of states—that connects polarity to its intellectual wellspring in realist thought. The question, at hand, is not how to treat behavior to allow for a more dynamic, complete, or empirically grounded systemic theory—maybe a theory in which systemic behavior is both cause and effect (Dessler, 1989)—but rather how to create a structurally sound theory of polarity. A potential reward for recognizing that capability is a key explanatory variable is (a) an awareness that “constructed” power cannot stray significantly or consistently from material realities before the two are brought back into harmony, and (b) a reduced danger of nonfalsifiable theory, modified or augmented (with qualifications and necessary conditions) solely to salvage an argument.

Admittedly, these guidelines fall short of a polarity theory, with an accompanying set of testable hypotheses. The point, however, is that scholars must stake their claim through empirical evidence only after grounding their concepts in theory—here, one in which cause and effect are clearly elucidated and differentiated. Although scholars have recognized polarity as a “theoretical concept,” they suggest the opposite when they assert that the “unprecedented” concentration of contemporary capabilities “should not prejudge questions about the extent and character of influence or about the logic of political relationships within the global system” (Ikenberry et al., 2011, p. 4). A theoretical concept requires the prejudging of relationships.


I wish to thank Eugene Gholz, Charles Glaser, William Wohlforth, and two anonymous reviewers for their very helpful comments on earlier manuscript drafts.


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(1.) As Wagner (1993, p. 85) argues, “the question of how to recognize a bipolar system is different from the question of how to define one, and common sense is no substitute for definition.”

(2.) These two statements are the basis, however, of two different definitions of unipolarity (Jervis, 2011, p. 255).

(3.) On unipolarity in academic discourse, see Hansen (2011, pp. 1–23).

(4.) Monteiro (2014, p. 167) actually acknowledges the limits of power projection in a two-war context.

(5.) As Levy (1985, pp. 44–45) notes, the behavioral indicators include “participation in international congresses and conferences; de facto identification as a Great Power by an international conference or organization; admission to a formal or informal organization of Powers, e.g., the Concert of Europe; participation in Great Power guarantees, territorial compensations, or partitions; and generally treatment as a relative equal by other Great Powers (e.g., protocol, alliances, negotiations, etc.).”

(6.) Viewed somewhat differently, hegemony “assigns a particular role for the lead state, a role accepted both domestically and internationally (Mowle & Sacko, 2007, p. 7).

(7.) For the litany of U.S. “offenses,” see Huntington (1999, p. 38).

(8.) On the distinction between these forms of balancing, see Layne (2006b, pp. 8–9).

(9.) On the “ironic” position of the preponderant state, see Mastanduno (1997, p. 55).

(10.) On the contemporary prevalence of international cooperation with the United States, and such cooperation as bandwagoning behavior, see Mowle and Sacko (2007, pp. 80–83).

(11.) On this, see Hempel (1952, p. 32).

(12.) That is, the implication, for example, when Jervis (2011, p. 252) asserts that “to say that the world is now unipolar . . . is to state a fact, but one whose meaning is far from clear.” To be fair, Jervis (2011, p. 254) also recognizes that “the best definitions do a great deal of theoretical work.”

(13.) Interestingly, scholars devoted much attention in prior decades to whether bipolarity or multipolarity was the more stable system. The effect was to focus the debate on first principles that would produce stability in one system and instability in the other. Unfortunately, the debate has not (as of yet) been carried fully into analyses of unipolarity.

(14.) Realism presents a useful starting point for analysis though Mowle and Sacko (2007, p. 31) are correct that “realists have minimized the possibility of a unipolar world.”

(15.) As Buzan (2004, p. 33) put it, in discussing bipolarity, “in one word it seemed to capture all of the main features that made the Cold War period different from what had come before.”

(16.) Polarity arguments draw implicitly, then, from the offensive realist conception of the security dilemma. Realists suppose, then, that states are wary of their standing relative to other states and act, by necessity, to offset their capabilities (Mearsheimer, 2001).

(17.) For just such an effort, see Mowle and Sacko (2007).

(18.) Buzan (2004, p. 33) maintains, however, that the concept polarity is consistent with a wide range of seemingly rival intellectual traditions “in a very different way, in systems composed either of rivals and friends, or just friends.”