Traditional notions of leadership are linked to the idea of the democratic nation-state, a sovereign entity capable of defending itself against foreign and domestic enemies. But the concept of the nation-state has been challenged, not only by ethnic and religious conflicts, but also by increased global mobility and the political integration of nation-states into international organizations--most prominently the European Union. In Citizenship in America and Europe, edited by AEI's Michael S. Greve and Michael Zoeller of the Council on Public Policy (AEI Press, 2009), scholars from both sides of the Atlantic consider how concepts of citizenship affect debates over immigration and assimilation, tolerance and minority rights, and national cohesion and civic culture. To what extent--if at all--should citizens' rights and duties change as the nation-state changes? [Read more.]