European politics and diplomacy in the 20th century were de ned by total war and its consequences. World War I destroyed the balance of power, and the Treaty of Versailles, which ended the war, created unstable conditions in which extremist ideologies emerged that challenged liberal democracy and the postwar settlement. In Russia, hardships during World War I gave rise to a revolution in 1917. The newly established, postwar democracies in central and eastern Europe were too weak to provide stability either internally or in the European state system, especially during the Great Depression of the 1930s. The League of Nations, established after the war to employ collective security in the interests of peace, could not manage the international tensions unleashed by World War I. The breakdown of the settlement led to World War II, a con ict even more violent than World War I. During this second great war, the combatants engaged in wholesale destruction of cities, deliberate attacks on civilians, and the systematic destruction of their enemies’ industrial complexes. The Nazi government in Germany undertook the annihilation of Jews from the whole continent (the Holocaust), as well as the murder of other targeted groups of Europeans. At the end of the war, the economic and political devastation left a power vacuum that facilitated the Cold War division of Europe.
During the 20th century, European imperialism, power, and sense of superiority reached both its apogee and nadir. In the rst half of the century, nations extended their control and influence over most of the non-Western world, often through League of Nations’ mandates. The idea of decolonization was born early in the century with the formation of movements seeking rights for indigenous peoples; the material and moral destruction of World War II made the idea a reality. After the war, regions colonized and dominated by European nations moved from resistance to independence at di ering rates and with di ering consequences. Yet even after decolonization, neocolonial dependency persisted, and millions of people migrated to Europe as its economy recovered from the war. This immigration created large populations of poor and isolated minorities, which occasionally rioted because of discrimination and economic deprivation. As European governments tried to solve these problems, the apparently permanent presence of the immigrants challenged old notions of European identity.
The uneasy alliance between Soviet Russia and the West during World War II gave way after 1945 to a diplomatic, political, and economic confrontation between the democratic, capitalist states of Western Europe allied with the United States and the communist bloc of Eastern Europe dominated by the Soviet Union (also known as the Union of Soviet Socialist Republics, or USSR). During the ensuing confrontation between East and West, called the Cold War, relations between the two blocs uctuated, but one consequence of the con ict was that European nations could not act autonomously in international a airs; the superpowers— the Soviet Union and the United States—controlled international relations in Europe.
Nonetheless, the Cold War promoted political and economic unity in Western Europe, leading to the establishment of a succession of ever-more comprehensive organizations for economic cooperation. In 1957, six countries formed the Common Market, which soon began to expand its membership to include other European states. The success of the Common Market inspired Europeans to work toward a closer political and economic unity, including a European executive body and Parliament. The founding of the European Union in 1991 at Maastricht included the agreement to establish the euro as a common currency for qualifying member- states. Following a series of largely peaceful revolutions in 1989, culminating in the collapse of the Soviet Union in 1991, the formerly communist states of Eastern Europe moved toward democracy and capitalist economies, and over time some of these states joined the European Union. One unforeseen consequence of the end of the Cold War was the re-emergence of nationalist movements within states, which led to the Balkan wars in Yugoslavia and tensions among the successor states of the Soviet Union as well as the rebirth of nationalist political parties in Western Europe.