The politics of the European Union's crises of the 2010s required the emergence of analyses and theorisation that sought to explain the possibility of European disintegration. This article makes a conceptual contribution to the emerging literature on European disintegration by arguing for the inclusion of nationalism as an important—yet under‐represented—variable in the politics and process of disintegration in the European Union. It draws together elements of enduring value in classical explanations of the rise and operation of nationalism in Europe from Ernest Gellner, Tom Nairn and John Breuilly, with a postfunctionalist emphasis on the politicisation of European Union politics at the member‐state level. The article concludes that a consideration of nationalism illuminates the process and politics of European disintegration by showing that the politics of European integration in the 2010s created nationalism rather than contained it, as it had been historically designed to do.