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{{short description|Way in which power is distributed within the international system}}
'''Polarity''' in [[international relations]] is any of the various ways in which [[power (international relations)|power]] is distributed within the international system. It describes the nature of the international system at any given period of time. One generally distinguishes three types of systems: '''unipolarity''', '''bipolarity''', and '''multipolarity''' for three or more centers of power.<ref>{{cite web|last1=Jiang|first1=Shiwei|title=Is Bipolarity a sound recipe for world order–as compared to other historically known alternatives. In ICD Annual Conference on Cultural Diplomacy in the USA Options on the Table," Soft Power, Intercultural Dialogue & the Future of US Foreign Policy. 2013|url=http://www.culturaldiplomacy.org/academy/content/pdf/participant-papers/2013-acdusa/Is-Bipolarity-a-sound-recipe-for-world-order-Shiwei-Jiang.pdf}}</ref> The type of system is completely dependent on the distribution of power and influence of [[state (polity)|states]] in a region or globally.

Scholars differ as to whether bipolarity or unipolarity is likely to produce the most stable and peaceful outcomes. [[Kenneth Waltz]] and [[John Mearsheimer]] are among those who argue that bipolarity tends to generate relatively more stability,<ref name=":1">{{Cite book|last=Waltz|first=Kenneth Neal|url=https://books.google.com/books?id=j6qOAAAAMAAJ|title=Theory of International Politics|date=1979|publisher=McGraw-Hill|isbn=978-0-07-554852-2|pages=170–171|language=en}}</ref><ref>{{Cite book|last=Mearsheimer|first=John|title=The Tragedy of Great Power Politics|publisher=W.W. Norton|year=2001|isbn=|location=|pages=44–45}}</ref>. In contrast, John Ikenberry and [[William Wohlforth]] are among those arguing for the stabilizing impact of unipolarity.<ref name="Wohlforth" /><ref name=":7">{{Cite book |last=Ikenberry |first=G. John |url=https://books.google.com/books?id=2IN0qin_p3MC |title=After Victory: Institutions, Strategic Restraint, and the Rebuilding of Order After Major Wars |date=2001 |publisher=Princeton University Press |isbn=978-0-691-05091-1 |language=en}}</ref> Some scholars, such as [[Karl Deutsch]] and [[J. David Singer]], argued that multipolarity was the most stable structure.<ref>{{Cite journal|last1=Deutsch|first1=Karl W.|last2=Singer|first2=J. David|date=1964|title=Multipolar Power Systems and International Stability|url=https://www.jstor.org/stable/2009578|journal=World Politics|volume=16|issue=3|pages=390–406|doi=10.2307/2009578|jstor=2009578|s2cid=53540403 |issn=0043-8871}}</ref>

The Cold War period was widely understood as one of bipolarity with the US and the USSR as the world's two [[superpower|superpowers]], whereas the end of the Cold War led to unipolarity with the US as the world's sole superpower in the 1990s and 2000s. Scholars have debated how to characterize the current international system.<ref name=":8">{{Cite news |date=2023-05-23 |title=Did the Unipolar Moment Ever End? |language=en-US |work=Foreign Affairs |url=https://www.foreignaffairs.com/ask-the-experts/did-unipolar-moment-ever-end |issn=0015-7120}}</ref><ref name=":9" />

==Unipolarity==
Unipolarity is a condition in which one state under the condition of international anarchy enjoys a preponderance of power and faces no competitor states.<ref name=":5">{{Cite journal |last=Monteiro |first=Nuno P. |date=2012 |title=Unrest Assured: Why Unipolarity Is Not Peaceful |url=https://doi.org/10.1162/ISEC_a_00064 |journal=International Security |volume=36 |issue=3 |pages=9–40 |doi=10.1162/ISEC_a_00064 |s2cid=57558611 |issn=0162-2889}}</ref><ref name=":02">{{Cite journal |last=Wohlforth |first=William C. |date=1999 |title=The Stability of a Unipolar World |url=https://www.jstor.org/stable/2539346 |journal=International Security |volume=24 |issue=1 |pages=5–41 |issn=0162-2889}}</ref> According to William Wohlforth, "a unipolar system is one in which a counterbalance is impossible. When a counterbalance becomes possible, the system is not unipolar."<ref name=":02" /> A unipolar state is not the same as an [[empire]] or a hegemon that can control the behavior of all other states.<ref name=":5" /><ref name="Jervis unipolar">{{cite journal |last=Jervis |first=Robert |date=2009 |title=Unipolarity: A Structural Perspective |url=http://muse.jhu.edu/journals/wp/summary/v061/61.1.jervis.html |journal=World Politics |volume=61 |issue=1 |pages=188–231, p. 190 |doi=10.1353/wp.0.0031 |quote=unipolarity implies the existence of many juridically equal nation-states, something that an empire denies}}</ref><ref name="Nexon Wright polarity">{{cite journal |last=Nexon |first=Daniel and Thomas Wright |date=2007 |title=What's at Stake in the American Empire Debate |journal=American Political Science Review |volume=101 |issue=2 |pages=253–271, p. 253 |citeseerx=10.1.1.136.2578 |doi=10.1017/s0003055407070220 |quote=in empires, inter-societal divide-and-rule practices replace interstate balance-of-power dynamics |s2cid=17910808}}</ref>

=== American primacy ===
Numerous thinkers predicted U.S primacy in the 20th century onwards, including [[William Ewart Gladstone|William Gladstone]],{{efn|[[Alexis de Tocqueville]] in the mid-19th century had expected the bipolar world centered on America and Russia but had not advanced beyond bipolarity.}}<ref>Cited in [[Hans Kohn]], “The US and Western Europe: A New Era of Understanding,” ''Orbis'', 6/1, (1962): p 17.</ref> [[Michel Chevalier]],<ref>Michel Chevalier, ‘La Guerre et la Crise Européenne’, ''Revue des Deux Mondes'', (1 June 1866), p. 784–785, https://fr.wikisource.org/wiki/La_Guerre_et_la_Crise_europ%C3%A9enne</ref> [[K'ang Yu-wei]],<ref name="Kang">[[K'ang Yu-wei]], (1885): ''The One World Philosophy'', (tr. Thompson, Lawrence G., London, 1958, pp. 79-85).</ref> [[Georges Vacher de Lapouge]],<ref name="GVdL">[[Georges Vacher de Lapouge]], ''L`Aryen: Son Role Social'', (Nantes, 1899: chapter "L`Avenir des Aryens," pp. XXXI-XXXII).</ref> [[H. G. Wells]] in ''[[Anticipations]]'' (1900),<ref>''[[Anticipations]]'', p 107.</ref> and [[William Thomas Stead]].

Liberal institutionalist [[John Ikenberry]] argues in a series of influential writings that the United States purposely set up an international order after the end of World War that sustained US primacy.<ref name="Ikenberry">{{cite journal |last=Ikenberry |first=G. John |date=Winter 1998–1999 |title=Institutions, Strategic Restraint, and the Persistence of American Postwar Order |journal=International Security |volume=23 |issue=3 |pages=43–78 |doi=10.1162/isec.23.3.43 |jstor=2539338 |s2cid=57566810}}</ref><ref name=":7" /> In his view, realist predictions of power balancing did not bear fruit because the United States engaged in strategic restraint after World War II, thereby convincing weaker states that it was more interested in cooperation rather than domination. U.S. strategic restraint allowed weaker countries to participate in the make-up of the post-war world order, which limited opportunities for the United States to exploit total power advantages. Ikenberry notes that while the United States could have unilaterally engaged in unfettered power projection, it decided instead to “lock in” its advantage long after zenith by establishing an enduring institutional order, gave weaker countries a voice, reduced great power uncertainty, and mitigated the [[security dilemma]]. The liberal basis of U.S. hegemony—a transparent democratic political system—has made it easier for other countries to accept the post-war order, Ikenberry explains. “American hegemony is reluctant, open, and highly institutionalized—or in a word, liberal” and “short of large-scale war or a global economic crisis, the American hegemonic order appears to be immune to would-be hegemonic challengers.”<ref name="Ikenberry" /><ref name=":7" />

=== Current debates ===
Scholars have debated whether the current international system is characterized by unipolarity, bipolarity or multipolarity.<ref name=":8" /><ref name=":9">{{Cite news |last=Brooks |first=Stephen G. |last2=Wohlforth |first2=William C. |date=2023-04-18 |title=The Myth of Multipolarity |language=en-US |work=Foreign Affairs |issue=May/June 2023 |url=https://www.foreignaffairs.com/united-states/china-multipolarity-myth |issn=0015-7120}}</ref> Michael Beckley argues American primacy is vastly underestimated because power indices frequently fail to take into account [[GDP per capita]] in the U.S. relative to other purportedly powerful states, such as China and India.<ref>{{Cite journal |last=Beckley |first=Michael |date=2018 |title=The Power of Nations: Measuring What Matters |url=https://direct.mit.edu/isec/article/43/2/7-44/12211 |journal=International Security |language=en |volume=43 |issue=2 |pages=7–44 |doi=10.1162/isec_a_00328 |issn=0162-2889 |doi-access=free}}</ref> In 2011, [[Barry Posen]] argued that unipolarity was in wane and that the world was shifting towards multipolarity.<ref>{{Citation |last=Posen |first=Barry R. |title=From unipolarity to multipolarity: transition in sight? |date=2011 |url=https://www.cambridge.org/core/books/international-relations-theory-and-the-consequences-of-unipolarity/from-unipolarity-to-multipolarity-transition-in-sight/CD35CD29F702546058795648A11748A1 |work=International Relations Theory and the Consequences of Unipolarity |pages=317–341 |editor-last=Ikenberry |editor-first=G. John |publisher=Cambridge University Press |isbn=978-1-107-01170-0 |editor2-last=Mastanduno |editor2-first=Michael |editor3-last=Wohlforth |editor3-first=William C.}}</ref> In 2019, John Mearsheimer argued that the international system was shifting from unipolarity to multipolarity.<ref>{{Cite journal |last=Mearsheimer |first=John J. |date=2019 |title=Bound to Fail: The Rise and Fall of the Liberal International Order |journal=International Security |volume=43 |issue=4 |pages=7–50 |doi=10.1162/isec_a_00342 |issn=0162-2889 |doi-access=free}}</ref>

In 2022, William Wohlforth argued that the international system was heading towards a system that can be characterized neither as bipolarity nor multipolarity. He added that polarity did not appear to matter as much in the current international system, as great powers command a far smaller share of power vis-a-vis the rest of the states in the international system.<ref>{{Citation |last=Wohlforth |first=William C. |title=Polarity and International Order: Past and Future |date=2022 |url=https://doi.org/10.1007/978-3-031-05505-8_21 |work=Polarity in International Relations: Past, Present, Future |pages=411–424 |editor-last=Græger |editor-first=Nina |series=Governance, Security and Development |place=Cham |publisher=Springer |language=en |doi=10.1007/978-3-031-05505-8_21 |isbn=978-3-031-05505-8 |editor2-last=Heurlin |editor2-first=Bertel |editor3-last=Wæver |editor3-first=Ole |editor4-last=Wivel |editor4-first=Anders}}</ref> In 2023, Wohlforth and Stephen Brooks argued that the United States is still the unipole but that US power has weakened and the nature of US unipolarity has changed.<ref name=":9" /> They add, "The world is neither bipolar nor multipolar, and it is not about to become either. Yes, the United States has become less dominant over the past 20 years, but it remains at the top of the global power hierarchy—safely above China and far, far above every other country... Other countries simply cannot match the power of the United States by joining alliances or building up their militaries."<ref name=":9" />

In April 2023, the Australian government released their 2023 national review where it is outright stated that the age of American unipolarity and primacy in the Indo-Pacific is effectively over, paving way to great power competition and a more fractious world order.<ref>{{Cite news |last=Needham |first=Kirsty |date=2023 |title=Australia to prioritise long-range strike capability in defence shake-up |url=https://www.reuters.com/world/asia-pacific/australia-prioritise-long-range-strike-capability-defence-shakeup-2023-04-24/}}</ref>

=== Impact on conflict and cooperation ===
Scholars have debated the durability and peacefulness of unipolarity. [[William Wohlforth]] argues that unipolarity is durable and peaceful because it reduces the likelihood of hegemonic rivalry (because no state is powerful enough to challenge the unipole) and it reduces the salience and stakes of balance of power politics among the major states, thus reducing the likelihood that attempts at balances of power cause major war.<ref name="Wohlforth">{{cite journal |last=Wohlforth |first=William |date=1999 |title=The Stability of a Unipolar World |journal=International Security |volume=24 |issue=1 |pages=5–41 |doi=10.1162/016228899560031 |s2cid=57568539}}</ref> Wohlforth builds his argument on [[hegemonic stability theory]] and a rejection of the [[Balance of power in international relations|balance of power]] theory.<ref name="Wohlforth" /> With no great power to check its adventurism, the United States will weaken itself by misusing its power internationally. “Wide latitude” of “policy choices” will allow the U.S. to act capriciously on the basis of “internal political pressure and national ambition.”<ref name="Waltz Structural Realism">{{cite journal |last=Waltz |first=Kenneth |date=Summer 2000 |title=Structural Realism after the Cold War |url=http://www.columbia.edu/itc/sipa/U6800/readings-sm/Waltz_Structural%20Realism.pdf |journal=International Security |volume=25 |issue=1 |pages=5–41 |doi=10.1162/016228800560372 |access-date=13 December 2012 |s2cid=57560180}}</ref>

According to [[Carla Norrlöf]], U.S. unipolarity is stable and sustainable due to a combination of three factors: 1. The status of the American dollar as the world's dominant [[reserve currency]], 2. American commercial power, and 3. American military preponderance. The United States benefits disproportionately from its status as hegemon. Other states do not challenge U.S. hegemony because many of them benefit from the U.S.-led order, and there are significant coordination problems in creating an alternative world order.<ref name=":0">{{Cite book |last=Norrlof |first=Carla |url=https://www.cambridge.org/core/books/americas-global-advantage/29F591B11AD3CCFDA25F7ED7D9191B55 |title=America's Global Advantage: US Hegemony and International Cooperation |date=2010 |publisher=Cambridge University Press |isbn=978-0-521-76543-5 |location=Cambridge |doi=10.1017/cbo9780511676406}}</ref>

[[Nuno P. Monteiro]] argues that unipolarity is conflict-prone, both between the unipole and other states, and exclusively among other states.<ref name="Monteiro">{{cite journal |last=Monteiro |first=Nuno |date=Winter 2011–2012 |title=Polarity and Power: U.S. Hegemony and China's Challenge |journal=International Security |volume=36 |issue=3 |doi=10.1162/ISEC_a_00064 |s2cid=57558611}}</ref> Monteiro substantiates this by remarking that “the United States has been at war for thirteen of the twenty-two years since the end of the Cold War. Put another way, the first two decades of unipolarity, which make up less than 10 percent of [[U.S. history]], account for more than 25 percent of the nation’s total time at war.”<ref name=":5" /> Kenneth Waltz that unipolarity is “the least durable of international configurations.”<ref>"Structural Realism After the Cold War," ''International Security'', 25/1, (2000): p 27.</ref> Secondly, even if the United States acts benevolently, states will still attempt to balance against it because the power asymmetry demands it: In a self-help system, states do not worry about other states’ intentions as they do other states' capabilities. “Unbalanced power leaves weaker states feeling uneasy and gives them reason to strengthen their positions,” Waltz says.<ref name="Waltz Structural Realism" />

In a 2009 study, [[Martha Finnemore]] argues that unipolarity has, contrary to some expectations, not given the United States a free rein to do what it wants and that unipolarity has proven to be quite frustrating for the United States. The reasons for this is that unipolarity does not just entail a material superiority by the unipole, but also a social structure whereby the unipole maintains its status through legitimation, and institutionalization. In trying to obtain legitimacy from the other actors in the international system, the unipole necessarily gives those actors a degree of power. The unipole also obtains legitimacy and wards off challenges to its power through the creation of institutions, but these institutions also entail a diffusion of power away from the unipole.<ref name=":6">{{Cite journal|last=Martha Finnemore|date=2009|title=Legitimacy, Hypocrisy, and the Social Structure of Unipolarity: Why Being a Unipole Isn't All It's Cracked Up to Be|url=http://dx.doi.org/10.1353/wp.0.0027|journal=World Politics|volume=61|issue=1|pages=58–85|doi=10.1353/wp.0.0027|issn=1086-3338}}</ref>

In a 2021 study, Yuan-kang Wang argues from the experience of [[Ming dynasty|Ming China]] (1368–1644) and [[Qing dynasty|Qing China]] (1644–1912) that the durability of unipolarity is contingent on the ability of the unipole to sustain its power advantage and for potential challengers to increase their power without provoking a military reaction from the unipole.<ref>{{Cite journal|last=Wang|first=Yuan-kang|date=2021|title=The Durability of a Unipolar System: Lessons from East Asian History|url=https://doi.org/10.1080/09636412.2020.1859127|journal=Security Studies|volume=29|issue=5|pages=832–863|doi=10.1080/09636412.2020.1859127|s2cid=231808778|issn=0963-6412|via=}}</ref>

== Bipolarity ==
{{Three worlds}}
{{Main|Balance of power (international relations)}}
Bipolarity is a distribution of power in which two states have a preponderance of power.<ref>{{Cite journal |last=Waltz |first=Kenneth N. |author-link1 = Kenneth Waltz |date=1964 |title=The Stability of a Bipolar World |url= https://www.jstor.org/stable/20026863 |journal= Daedalus |volume=93 |issue=3 |pages=881–909 |jstor= 20026863 |issn= 0011-5266}}</ref> In bipolarity, spheres of influence and alliance systems have frequently developed around each pole. For example, in the [[Cold War]] of 1947-1991, most Western and capitalist states would fall under the influence of the US, while most Communist states would fall under the influence of the [[USSR]]. According to Wohlforth and Brooks, "the world was undeniably bipolar" during the Cold War.<ref name=":9" />

Historic examples of bipolarity include [[Kingdom of Great Britain|Great Britain]] and [[Kingdom of France|France]] in 18th century from the end of the [[War of the Spanish Succession]] (1701-1715) until the [[Seven Years' War]] (1754-1763), and the [[United States]] and the [[Soviet Union]] during the [[Cold War]] (1947-1991).

=== Impact on conflict and cooperation ===
Kenneth Waltz's influential ''[[Theory of International Politics]]'' argued that bipolarity tended towards the greatest stability because the two great powers would engage in rapid mutual adjustment, which would prevent inadvertent escalation and reduce the chance of power asymmetries forming.<ref name=":1" /> John Mearsheimer argues that bipolarity is the most stable form of polarity, as buck passing is less frequent.<ref>{{Cite book |last=Mearsheimer |first=John J. |url= |title=The Tragedy of Great Power Politics |date=2001 |publisher=W. W. Norton & Company |isbn=978-0-393-34927-6 |language=en |chapter=Chapter 9}}</ref> Dale Copeland has challenged Waltz on this, arguing that bipolarity creates a risk for war when a power asymmetry or divergence happens.<ref>{{Cite journal |last=Copeland |first=Dale C. |date=1996 |title=Neorealism and the myth of bipolar stability: Toward a new dynamic realist theory of major war |url=https://doi.org/10.1080/09636419608429276 |journal=Security Studies |volume=5 |issue=3 |pages=29–89 |doi=10.1080/09636419608429276 |issn=0963-6412}}</ref>

== Multipolarity ==
Multipolarity is a distribution of power in which more than two states have similar amounts of power. The [[Concert of Europe]], a period from after the [[Napoleonic Wars]] to the [[Crimean War]], was an example of peaceful multipolarity (the great powers of Europe assembled regularly to discuss international and domestic issues),<ref>{{Cite news |last1=Haass |first1=Richard |last2=Kupchan |first2=Charles A. |date=2021-04-29 |title=The New Concert of Powers |language=en-US |journal=Foreign Affairs |url=https://www.foreignaffairs.com/articles/world/2021-03-23/new-concert-powers |access-date=2021-10-25 |issn=0015-7120}}</ref> as was the [[Interwar period]].<ref name=":4">{{Cite book |last=Sullivan |first=Michael P. |url=https://books.google.com/books?id=YfxeCwAAQBAJ |title=Theories of International Relations : Transition vs Persistence |publisher=Palgrave Macmillan |others=S. Burchill |year=2001 |isbn=1-281-36762-1 |pages=128 |oclc=815569732}}</ref> Examples of wartime multipolarity include [[World War I]],<ref>{{Cite web |title=A dangerous history of multipolarity |url=https://www.lowyinstitute.org/the-interpreter/dangerous-history-multipolarity |access-date=2021-10-25 |website=www.lowyinstitute.org |language=en}}</ref> [[World War II]],<ref>{{Cite journal |last=Schweller |first=Randall L. |date=1993 |title=Tripolarity and the Second World War |url=https://www.jstor.org/stable/2600832 |journal=International Studies Quarterly |volume=37 |issue=1 |pages=73–103 |doi=10.2307/2600832 |issn=0020-8833 |jstor=2600832}}</ref> the [[Thirty Years War]],<ref>{{Cite journal |last1=Midlarsky |first1=Manus I. |last2=Hopf |first2=Ted |date=1993 |title=Polarity and International Stability |url=https://www.jstor.org/stable/2938964 |journal=The American Political Science Review |volume=87 |issue=1 |pages=171–180 |doi=10.2307/2938964 |issn=0003-0554 |jstor=2938964|s2cid=145530074 }}</ref> the [[Warring States period]],<ref>{{Cite web |title=China Debates the Future Security Environment |url=https://nuke.fas.org/guide/china/doctrine/pills2/part03.htm |access-date=2021-10-25 |website=nuke.fas.org}}</ref> the [[Three Kingdoms]] period and the tripartite division between [[Song dynasty]]/[[Liao dynasty]]/[[Jin dynasty (1115–1234)|Jin dynasty]]/[[Yuan dynasty]].

=== Impact on conflict and cooperation ===
[[File:World empires and colonies around World War I.png|thumb|upright=1.35|right|Empires of the world in 1905, with minor mistakes]]

[[Political realism|Classical realist]] theorists, such as [[Hans Morgenthau]] and [[E. H. Carr]], hold that multipolar systems are more stable than bipolar systems, as great powers can gain power through alliances and petty wars that do not directly challenge other powers; in bipolar systems, classical realists argue, this is not possible.

[[neorealism (international relations)|Neorealists]] hold that multipolar systems are particularly unstable and conflict-prone, as there is greater complexity in managing alliance systems, and a greater chance of misjudging the intentions of other states.<ref>{{Cite journal |last=Jervis |first=Robert |date=1978 |title=Cooperation Under the Security Dilemma |url=https://www.jstor.org/stable/2009958 |journal=World Politics |volume=30 |issue=2 |pages=167–214 |doi=10.2307/2009958 |jstor=2009958 |hdl=2027/uc1.31158011478350 |s2cid=154923423 |issn=0043-8871|hdl-access=free }}</ref> [[Thomas J. Christensen|Thomas Christensen]] and [[Jack Snyder (political scientist)|Jack Snyder]] argue that multipolarity tends towards instability and conflict escalation due to "chain-ganging" (allies get drawn into unwise wars provoked by alliance partners) and "buck-passing" (states which do not experience an immediate proximate threat do not balance against the threatening power in the hope that others carry the cost of balancing against the threat).<ref>{{Cite journal|last1=Christensen|first1=Thomas J.|last2=Snyder|first2=Jack|date=1990|title=Chain Gangs and Passed Bucks: Predicting Alliance Patterns in Multipolarity|url=https://www.jstor.org/stable/2706792|journal=International Organization|volume=44|issue=2|pages=137–168|doi=10.1017/S0020818300035232|jstor=2706792|s2cid=18700052 |issn=0020-8183}}</ref> John Mearsheimer also argues that buck passing is more common in multipolar systems.<ref>{{Cite book |last=Mearsheimer |first=John J. |url= |title=The Tragedy of Great Power Politics |date=2001 |publisher=W. W. Norton & Company |isbn=978-0-393-34927-6 |language=en |chapter=Chapter 8}}</ref>

Multipolarity does not guarantee [[multilateralism]] and can pose a challenge against multilateralism.<ref name=":2">{{Cite web|last=Derviş|first=Kemal|date=2018-07-23|title=Can multilateralism survive?|url=https://www.brookings.edu/opinions/can-multilateralism-survive/|access-date=2021-10-25|website=Brookings|language=en-US}}</ref><ref name=":3">{{Cite journal|last=Hoekman|first=Bernard|date=2014-06-01|title=Sustaining multilateral trade cooperation in a multipolar world economy|url=https://doi.org/10.1007/s11558-014-9187-3|journal=The Review of International Organizations|language=en|volume=9|issue=2|pages=241–260|doi=10.1007/s11558-014-9187-3|hdl=1814/28962|s2cid=154578416|issn=1559-744X}}</ref> According to [[Kemal Derviş]], a decline in unipolarity creates a crisis in multilateralism; it is possible to revive multilateralism in a multipolar system, but this is more threatened and the structure to do so is not fully developed.<ref name=":2" /> In multipolarity, larger powers can negotiate "mega-regional" agreements more easily than smaller ones. When there are multiple competing great powers, this can lead to the smaller states being left out of such agreements.<ref name=":3" /> Though multipolar orders form regional hegemonies around 'poles' or great powers, this can weaken economic interdependencies within regions, at least in regions without a great power.<ref>{{Cite journal|last=Garzón|first=Jorge F.|date=2017|title=Multipolarity and the future of economic regionalism|url=https://www.cambridge.org/core/journals/international-theory/article/abs/multipolarity-and-the-future-of-economic-regionalism/0418032901079B335295729FA020CC92|journal=International Theory|language=en|volume=9|issue=1|pages=101–135|doi=10.1017/S1752971916000191|s2cid=151415696|issn=1752-9719}}</ref> Additionally, as multipolar systems can tend to regional hegemonies or bounded orders, agreements are formed within these bounded orders rather than globally. Though, Mearsheimer predicts the persistence of a thin international order within multipolarity, which constitutes some multilateral agreements.<ref>{{Cite journal|last=Mearsheimer|first=John J.|date=2019-04-01|title=Bound to Fail: The Rise and Fall of the Liberal International Order|url=https://doi.org/10.1162/isec_a_00342|journal=International Security|volume=43|issue=4|pages=7–50|doi=10.1162/isec_a_00342|s2cid=139105003|issn=0162-2889|doi-access=free}}</ref>

== Measuring the power concentration ==
The [[Correlates of War]] uses a systemic concentration of power formula to calculate the polarity of a given [[great power]] system. The formula was developed by [[J. David Singer]] et al. in 1972.<ref name="mansfield">{{cite journal |last=Mansfield |first=Edward D. |author-link=Edward Deering Mansfield |date=March 1993 |title=Concentration, Polarity, and the Distribution of Power |journal=International Studies Quarterly |volume=37 |issue=1 |pages=105–128 |doi=10.2307/2600833 |jstor=2600833 }}</ref>

: <math> \text{Concentration}_t = \sqrt{\frac{\sum_{i=1}^{N_t} (S_{it})^2 - \frac{1}{N_t}}{1 - \frac{1}{N_t}}}</math>

:''t'' = the time at which the concentration of resources (i.e. power) is being calculated
:''i'' = the state of which the proportion of control over the system's power is being measured
:''N''<sub>''t''</sub> = the number of states in the great power system at time ''t''
:''S'' = the [[Ratio|proportion]] of power possessed. Hence, ''S''<sub>''it''</sub> = the proportion of power possessed by state ''i'' at time ''t''.

The expression <math>\sum_{i=1}^n (S_{it})^2</math> represents the sum of the squares of the proportion of power possessed by all states in the great power system.

The closer the resulting concentration is to zero, the more evenly divided power is. The closer to 1, the more concentrated power is. There is a general but not strict correlation between concentration and polarity. It is rare to find a result over 0.5, but a result between 0.4 and 0.5 usually indicates a unipolar system, while a result between 0.2 and 0.4 usually indicated a bipolar or multipolar system. Concentration can be plotted over time, so that the fluctuations and trends in concentration can be observed.

== See also ==
* [[Balance of power (international relations)]]
* [[Global policeman]]
* [[International monetary systems]]
* [[Non-Aligned Movement]]
* [[Pax Americana]]
* [[Pax Britannica]]
* [[Power (international relations)]]
* [[Posthegemony]]
* [[Regional hegemony]]
* [[Thucydides Trap]]

==Bibliography==
* Thompson, William R. ''On Global War: Historical–Structural Approaches to World Politics.'' Columbia, SC: University of South Carolina Press, 1988, pp. 209–210.

==Notes==
{{notelist}}

==References==
{{Reflist|2}}

==External links==
*[http://www.drgi.com/globalpowerbarometer.html Global Power Barometer]

{{International power}}

{{DEFAULTSORT:Polarity In International Relations}}
[[Category:International relations theory]]

Polarity (international relations) - Revision history

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