The so-called refugee crisis has triggered a broad and divisive political discussion about overrun national borders, crumbling state sovereignty, and the disintegration of democratic governance resulting from an alleged disregard for the law by the German Federal Government. Many critics have advanced arguments that are nothing more than hot-tempered polemics based on blunt legal or theoretical misconceptions. Nonetheless, it is obvious that external boundaries played—and will continue to play—a pivotal role in managing the inflow of migrants into the European Union, which is surrounded by areas of political instability, authoritarianism, poverty, civil war, and religious extremism. This Article addresses the function of territorial borders for a liberal democracy from the perspective of constitutional theory. It demonstrates that effectively controlled outer boundaries are an adequate democratic answer to an instable, fragmented, and fragile world, while avoiding the pitfalls of defining political and social membership by substantive and inescapable criteria, such as ethnicity.