With a population of nearly 450 million people and the world’s third-largest economy, after the United States and China, the European Union (EU) appears to possess the fundamentals necessary to become a major world power. But unlike the US or China, the EU is not a single state. Rather, it is a unique assortment of supranational institutions that attempt to coordinate policy between 27 member states. Dating back to the 1950s, this long-running project of European integration has been more successful in some areas than others. The EU has succeeded in establishing a common currency, internal market, and free movement within the Schengen Area that includes most member states, for example, but remains without a common defense or foreign policy. As American hegemony recedes and the world becomes more multipolar, the ability of Europe to meet its geopolitical aims will increasingly depend on cohesion at the supranational level. Evaluating European integration helps clarify whether a united Europe will be a key global player in the future or, alternately, a disunited Europe will increasingly flounder in competition with China, Russia, Turkey, and others.