The text explains the main topics and conceptual arguments of the theme issue on the diverse reception of Ratzel's spatial theories in Italy, France, Germany and the USA. The focus is both on the different national academic traditions and on an interdisciplinary approach. The work and impact of Friedrich Ratzel between 1880 and 1945 are examined in the perspective of a history of transformation based on the history of knowledge.

At the end of XIXth century, French authors shared a posture that mixed admiration and criticism toward German science. Reference to Ratzel was used both for structuring human geography and feeding a struggle between geographers and other social scientists. Divergences with Ratzel’s work deepened during the war and lead geographers to revisit his key notion, Raum, by giving it a pragmatic sense in the light of pangermanism and interpreting it not as mere expanse but as a process of enlargement.

This article analyses the transformation of geographic, international legal and racial-biological relations within large-scale theories. The change in discourse implies the question of the extent to which geographical knowledge was relevant for the Nazi extermination policy; at the same time, the focus is on the shift from a description of human communities based on natural laws to an action-based programme of racial-biological homogenization.

The French geographers of the inter-war period considered the figure of Ratzel with admiration and criticism and tried to go beyond his work, and even to use it against his heirs, in particular the supporters of Geopolitik. Throughout the crises and world wars that gave him a persistent relevance, his image oscillated between that of a precursor scholar and a bad teacher of geography, largely responsible for Germany's excesses and territorial ambitions.

The paper examines the contribution of Italian academic geography to the processes of nation-building between ca. 1880–1920, especially in defining the national space and its boundaries. Italian geographers were particularly influenced by new approaches introduced by German scholars such as Friedrich Ratzel. Scientific theories and representations proved highly significant in influencing the political debate.

The relevance of the outbreak of the First and Second World Wars to the posthumous reception of Ratzel's work cannot be overestimated; Kjellen in particular was one of the main protagonists of Ratzel's revival. Kjellen and Schmitt appropriated and transformed Ratzel's concepts for their research aims, in order to highlight a new turning point in the political and juridical sciences and in politics. As a consequence, their Ratzel was oriented toward militant aims.

The paper explores the reception and re-elaboration of Friedrich Ratzel's political geography in Italy from the beginning of the 20th century to the Second World War, by focusing on the concept of spazio vitale (living space) and its use by fascist intellectuals and propagandists, who promoted expansionism and the trilateral collaboration with Germany and Japan.

This paper examines the intellectual relationship between the influential American geographer Ellen Churchill Semple and her professor, the German geographer Friedrich Ratzel. Semple clearly developed her own theory of anthropogeography from a reading of Ratzel. But she did so in a political context, i.e. post-slavery North America. Her theory clearly expresses that context and her dissatisfaction with particular elements in Ratzel's corpus.