Polarity (international relations)

Bruce Bueno de Mesquita has argued that the correlation between polarity of any kind and conflict is statistically weak, and depends critically on systemic uncertainty and risk attitudes among individual actors. Jeffrey Legro has argued that polarity is not among the foremost factors in explaining world politics, noting that ideational factors also matter in world politics. ==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. 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." American primacy Numerous thinkers predicted U.S. primacy in the 20th century onwards, including William Gladstone, Michel Chevalier, Kang Youwei, Georges Vacher de Lapouge, H. G. Wells in Anticipations (1900), 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 II that sustained U.S. primacy. 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. He has argued that the current international system is not characterized by "multipolarity but stark asymmetry: one consolidated American sphere and contested space everywhere else." In 2019, John Mearsheimer argued that the international system was shifting from unipolarity to multipolarity. 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. In 2023, Wohlforth and Stephen Brooks argued that the United States is still the unipole but that U.S. power has weakened and the nature of U.S. unipolarity has changed. Wohlforth builds his argument on hegemonic stability theory and a rejection of the balance of power theory. Bruce Bueno de Mesquita has argued that the correlation between polarity of any kind and conflict is statistically weak, and depends critically on systemic uncertainty and risk attitudes among individual actors. Nuno P. Monteiro argues that unipolarity is conflict-prone, both between the unipole and other states, and exclusively among other states. 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." 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. In a 2021 study, Yuan-kang Wang argues from the experience of Ming China (1368–1644) and 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. == Bipolarity ==

Bipolarity is a distribution of power in which two states have a preponderance of power. In bipolarity, spheres of influence and alliance systems have frequently developed around each pole. For example, in the Cold War, most Western and capitalist states would fall under the influence of the USA, 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. Tang and the Umayyad Caliphate during the Muslim conquest of Transoxiana, Spain and the Ottoman Caliphate (1517–1635), Great Britain and France in the 18th century from the end of the War of the Spanish Succession (1701–1715) to the Seven Years' War (1754–1763) and the French Revolutionary and Napoleonic Wars (1792–1815), 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. Dale C. Copeland has challenged Waltz on this, arguing that bipolarity creates a risk for war when a power asymmetry or divergence happens. == 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), as was the Interwar period. Examples of wartime multipolarity include World War I, World War II, the Thirty Years War, the Warring States period, the Three Kingdoms period, and the tripartite division between the Song, Liao, and Jin dynasties, prior to their fall at the behest of the emerging Yuan dynasty. Impact on conflict and cooperation 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. 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. Thomas Christensen and 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). John Mearsheimer also argues that buck passing is more common in multipolar systems. Multipolarity does not guarantee multilateralism and can pose a challenge against multilateralism. 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. 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. The term multipolarity has been used to describe the development of close relations between China and the Russian Federation after the Cold War, emerging out of the shared goal to disrupt American leadership in the international system. According to Edina Julianna Haiszky, the Russian-Chinese alliance to create a multipolar international system is informed by their self-perception as independent civilisations rather than nation-states, precipitating a political desire to act as active shapers of the international system. == 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. : \text{Concentration}_t = \sqrt{\frac{\sum_{i=1}^{N_t} (S_{it})^2 - \frac{1}{N_t}}{1 - \frac{1}{N_t}}} :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 :Nt = the number of states in the great power system at time t :S = the proportion of power possessed. Hence, Sit = the proportion of power possessed by state i at time t. The expression \sum_{i=1}^n (S_{it})^2 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 ==