International football has often been described as a soft way for nations to go to war. This analysis is too simplistic, but the reference to warfare is not uninteresting and provides the starting point for this dissertation. Having noticed the national fervour surrounding international football, and recognised warfare’s nationalist builder power, it seeks to explore the extent to which international football and international war are comparable in building nationalism. It adopts an ethno-symbolist perspective on nations and nationalism, hence seen as modern constructions rooted in more ancient cultures and groups. It argues that international football and international war are, indeed, using the same mechanisms to build nationalism, but that this comparison might evolve with globalisation, and, especially, the associated immigration flows and diasporas. More precisely, the first part of the answer argues that within the traditional framework of the nation-state, myth building, tradition shaping, and rivalry constructions are nationalist elements shared by international war and football. The second part is more hypothetical and seeks to explore how football can be a new nationalism vector for diasporas, linking national groups no longer sharing a unique territory. This dissertation illustrates each point with two case studies: a small set of detailed interviews with Dutch people to analyse the importance of football myths in building their nationalism, and a questionnaire, carried online and in person near Paris, with 46 members of the Portuguese community in France, to understand how the role of football in building nationalism might evolve.