At the end of World War I, peace treaties wiped the Austro-Hungarian Empire off the map, and as a result of the Treaty of Trianon on June 4, 1920, the Kingdom of Hungary was dismembered. As a part of this process, a thin band of mainly German-speaking territory of some 4000 km2, West-Hungary, became a part of Austria. This paper investigates both the arguments used by Hungarian geographers in defence of that country's territorial unity, notably those aimed at retaining and potentially recovering West-Hungary, and the arguments used by Austrian and German geographers to justify the annexation of that area. Analysing published and unpublished sources (articles, books, maps, propaganda material, and popular science literature), we show that scholars from both sides of the new border based their detailed arguments on similar theories, and used the same methods and mapping technologies for their own causes. We demonstrate that geographical arguments and analyses cannot be divorced from their political context, and that the politics of the new Europe that emerged after 1918 were profoundly geographical in nature.