To what extent do we still need nation-states? We tend to imagine that they have always existed and always will, but they are a recent phenomenon, and could be a temporary one. A study by the journalist Debora MacKenzie explains that, before the late eighteenth century, there were no clear national boundaries, and no border checks. Even in the nineteenth century, many Europeans could not name the nation to which they belonged. The locus of attachment for most people was their village or town. The discrete nation-state developed in response to rising industrial and social complexity. [...]