The Westphalian system of sovereign nation-states is being challenged as national administrations lose their 'gate-keeper-role' between domestic and international politics. But what kind of political system is emerging 'after Westphalia'? The article attempts to answer this question by looking at processes of political institution-building in cross-border regions in Europe and North America. A classification of political institutions is developed which, in a first dimension, distinguishes between instrumental and identity-providing institutions. Second, formal, encompassing and territorially based political institutions are contrasted with informal, specific and non-territorial institutions. Based on this classification, the forms of cross-border collaboration in four border regions in Europe and North America are compared. In Europe, cross-border collaboration is producing another soft, but formalized, comprehensive and territorially defined layer in the European 'multi-level-system'. In North America, by contrast, only informal, specific and non-territoral institutions are evolving across the national borders. Here, the territorially based nation-state is not complemented by similar kinds of polities, but is instead being challenged more fundamentally by new kinds of polities - transnational socio-economic exchange networks and transnational ideological coalitions which embody enormous transformational potential.
