Why are things different on the other side of national borders; and how can this be explained sociologically? This inaugural lecture tries to answer these questions, starting from the example of the bicycle in the Netherlands. It distinguishes four processes that have contributed to increasing similarity within nations: growing interdependence within nations; increasing density of networks and institutions; vertical diffusion of styles and standards; and the development of national we-feelings. Together, these processes have contributed to the development of national habitus: increasing similarities within nations, and increasing differences between people living in different countries. These processes have reached their apex in the second half of the twentieth century. Since then, they have diminished, leading to increasing variations within countries, and growing similarities between comparable groups in different countries. This analysis poses new questions and challenges for sociologists. First, it leads us to rethink comparative research: what are we comparing when we compare nations, and is this still a viable unit of analysis? Second, it leads us to consider how the transfer of styles and standards occurs in our informalized, globalized, and mediatized age. Third, sociologists should analyse the new forms of inequality resulting from these processes, such as the growing rift between ‘locals’ and (bike-loving) cosmopolitans.