Foreign policy experts have struggled to describe the unusual character of contemporary world politics. Much of the debate revolves around the concept of polarity, which deals with how power is distributed among nations, as experts ask if the United States is still a unipolar power or in decline as new powers emerge. The polarity debate, however, obscures more than it clarifies because the distribution of power does not determine the fate of nations by itself. It leaves out strategic choice and does not predict how the United States would exercise its power or how others would respond to U.S. primacy. World politics can take many paths, not just one, under any particular distribution of power. The most remarkable feature of post-Cold War world politics has not been the much-discussed power accumulation of the United States—although that is indeed noteworthy—but rather the absence of counter- balancing and revisionist behavior by other major powers.
Recently, we have seen the return of both balancing behavior (i.e. efforts to deter or defeat the United States) and revisionism (i.e. efforts to change the status quo) by Russia and China. Moscow has sought to prevent the further expansion of the European Union and NATO through military interventions and coercive diplomacy in Georgia, Ukraine, and Armenia. It revised the map of Europe by annexing Crimea, which was the first act of irredentism there since World War II. And it has launched countless provocations—such as incursions into air and maritime space—against NATO and EU member states including Latvia, Estonia, Lithuania, Sweden, Finland, and Denmark. Russia has also actively built up its military capacity to more effectively carry out balancing and revisionist strategies by means of special operations and unconventional warfare. For its part, China has sought to revise the maritime status quo in the South China Sea through aggressive operations in the Scarborough Shoal, the second Thomas Reef, and in Vietnamese waters, as well as by flexing its muscles in the East China Sea and elsewhere. It is also actively balancing against the United States by means of a major military build-up, especially with asymmetric weapons to blunt U.S. power projection capabilities.
In an effort to explain the prior absence and current return of counterbalancing, great power revisionism, and the implications for U.S. grand strategy, I argue that what we have seen is the rise and fall of a Unipolar Concert, similar to the Concert of Europe in the 19th century. Whereas the Concert of Europe was essentially a bipolar arrangement, with the co-hegemonies of Russia and Britain standing atop all others, the Unipolar Concert saw the United States set the agenda with others following suit.
For a generation, U.S. strategic thinking has been heavily conditioned by the rise and existence of the Unipolar Concert—successive presidents saw geopolitical competition as a thing of the past and focused on international cooperation to tackle shared challenges such as terrorism and nonproliferation. The demise of the Unipolar Concert marks the return of geopolitical competition and presents a significant challenge for U.S. strategy.
For more on this topic, read this article published in The Washington Quarterly.
 The literature on American decline is vast. For the view that the United States is in relative decline see Fareed Zakaria, The Post-American World (New York, NY: Norton, 2008); Charles Kupchan, No One’s World: The West, The Rising Rest, and The Coming Global Turn (New York, NY: Oxford University Press, 2012); and Kishore Mahbubani, The New Asian Hemisphere: The Irresistible Shift of Global Power to the East (New York, NY: Public Affairs, 2008). For the argument that the United States is not in decline see Joseph Joffe, The Myth of America’s Decline: Politics, Economics, and a Half Century of False Prophecies (Liveright Publishing, 2013); and Robert Lieber, Power, Willpower, and the American Future (London: Cambridge University Press, 2012).