Abstract
The processes of building the United States of America (US) during the nineteenth century and the European Union (EU) since the mid-twentieth century are among the major claims for the possibility of a vast, ‘imperial’-size political unit based on democratic principles. Although the American Union was designed by the late eighteenth century, the crucial period for its consolidation was between the Civil War and the World War I, when it established clear territorial limits and completed its internal institutionalization as a federal democratic union. After more than 50 years of increasing integration, the EU has achieved higher levels of economic integration on some issues than the US did 100 years ago, but it still recognizes a number of additional candidates to become member-states and has not attained a stable constitutional framework. In both cases putting an end to the process of territorial expansion and fixing neat external frontiers seems to be a necessary condition to achieve internal institutional stability and robust federal formulas.