Summary

Bipolarity was viewed both as an empirical condition and as a central explanatory concept, albeit contested, during the Cold War (1945–1989), when two superpowers dominated the international system. The United States and the Union of Soviet Socialist Republics (USSR) confronted each other as military and ideological rivals heading competing alliance systems—the North Atlantic Treaty Organization (NATO), founded in 1949, and the Warsaw Pact established in 1955. Nuclear weaponry added a new wrinkle to the global superpower competition, particularly after the Soviet Union broke the American nuclear monopoly in 1949. A rich literature around these themes emerged as scholars sought to grapple with the explanatory dynamics propelling state behavior under the systemic constraints of bipolarity and the technological challenges presaged by the nuclear age. Such an academic focus meant that the study of international politics, particularly in the United States, was largely refracted through the prism of U.S.-Soviet competition and centered on the nature and implications of polarity, power, alliances, and nuclear deterrence. When the Soviet Union imploded, bipolarity in the sense of two predominant powers ended, as did the division of the world into two opposing blocs. In the post-Cold War period, scholars turned their attention to investigating questions regarding the impact on the nature of system structure and the international order of the collapse of one of the poles.

Accordingly, during the Cold War, scholars debated the conceptual and empirical understandings of bipolarity as well as its implications and the causal factors on which the expectation of bipolar stability was based. In the post-Cold War period, scholars reflected over whether the end of ideological (capitalism/democracy vs. communism/single party authoritarianism) conflict presaged the end of history or inaugurated a clash of civilizations, with some questioning the salience of the concept of polarity and the viability of the state system in the face of rising subnational and transnational pressures.