The successive construction of the Maginot Line and the West Wall marked a critical moment in the militarization of the Franco-German frontier during the interwar period. Building the massive fortifications necessitated a nationwide mobilization of material, manpower, and public opinion in France and Germany. The effort fundamentally disrupted the fabric of life at the local level on both sides of the border, blurring the line between war and peace and continuing to reverberate after hostilities commenced on September 1, 1939. In his sweeping comparative and transnational history of “war in peacetime” and “peace in wartime,” Johannes Groβmann asks how societies and spaces transform through preparing for and prosecuting military conflict (12). The book traces the evolving and contextually dependent local and national understandings of the Franco-German frontier from the nineteenth century to the present. Yet its primary analytical focus revolves around the interwar fortifying of the borderland, the preventative civilian evacuations in September 1939, and the reordering of the region during the Second World War. Groβmann builds upon the work of the Franco-German research project Les évacuations dans l'espace frontalier franco-allemand 1939-1945 (2012-2015), the work of Henri Lefebvre, and extensive archival sources to highlight individual experience and move beyond a regime-level comparison of France and Nazi Germany.

Late-nineteenth- and early-twentieth-century French and German conceptions of the border were influenced by a combination of scientific, intellectual, and political currents, and martial conflict. The fortification of the Franco-German frontier embodied these competing impulses as well as both governments’ different contemporary ideological goals. The Maginot Line, begun in the 1920s and completed in the 1930s, developed out of a military fortification tradition, strategic lessons from the First World War, determination to prevent a recurrence of the 1914-1918 occupation, and the desire to alleviate the contemporary economic crisis in France. Begun in 1938 under more secretive circumstances, the West Wall's contrasting building speed, poorer workmanship, and incompleteness testify to its primary purpose towards mobilizing Germany for war. Both military defenses disrupted borderland residents’ lives to different degrees. Yet the militarization of everyday life and a growing sense of insecurity associated with an awareness of the heightened potential for military conflict were shared experiences. War is not a phenomenon absent one day and present the next. As Groβmann adroitly demonstrates, the construction of the Maginot Line and the West Wall, and the concurrent national propaganda campaigns, metamorphosed the Franco-German borderland in the public mind into a “red zone” with real consequences for governmental policy and local inhabitants before the outbreak of hostilities (123). Reconceptualizing conflict periodization, particularly concluding dates, has been the focus of much recent First World War historiography on the East European and Russian lands. Zwischen Fronten suggests a similar need to reevaluate hostilities’ beginnings by examining the spaces where martial preparations are first evident, their influence upon subsequent state programs, and unofficial actors’ associated experiences.

The outbreak of the Second World War witnessed a new frontier transformation. Prewar plans snapped into action and, in what Groβmann identifies as the first mass migration of the Second World War, 1.2-1.6 million borderland residents were removed to the interior in anticipation of imminent fighting. French authorities consciously tried to maintain evacuee communities by transplanting them to propinquitous interior areas. German officials sought to clear the border region for military operations quickly and subsequently scattered evacuees with little attention to local or familial ties. Displaced people's experiences were not uniform, varying according to their urban or rural background, religious denomination, age, health, gender, and social class. Constructing the fortifications and evacuations facilitated larger debates about national belonging and exclusion. Ironically, the migrations underscored “internal societal borders” within the nation at a time when state authorities stressed the need for solidarity (457). Evacuees often appeared “foreign” to interior residents, who labeled the newcomers “Boches” or “Halbfranzosen”. Frequent misunderstandings and clashes disillusioned many border dwellers and (re)confirmed the importance of their home communities and local identities.

Recent scholarship has called for greater recognition of Germany’s western frontier with France as a key site for shaping national identity and inspiring broader state policy. Sarah Frenking argues that Germans began imagining a bordered national community on the Franco-German boundary rather than the eastern marches during the Kaiserreich (Zwischenfälle im Reichsland [2021]). Groβmann's analysis similarly shifts geographic focus to argue that the West served as the laboratory for later Nazi population and occupation policies. The wartime annexation of Alsace and Lorraine radically altered the space and demographics of the borderland. German officials sought to rebuild and repopulate the former frontier according to National Socialist ideals. Their war preparations and civilian evacuations along the French boundary in 1939 acted as a radicalizing catalyst for subsequent eugenic and anti-Semitic measures within Germany. Thus, patients displaced from sanatoria and nursing homes became some of the first victims of the T4 program. Jewish evacuees were permitted housing only with fellow Jews and forbidden from returning to their borderland homes. The “new ordering” of the former French territories served as a model for the administrative incorporation of other conquered European lands after 1940 (365). Parallel efforts to repopulate the one-time frontier with “desirable” interior settlers and a destructive Germanization campaign speak to the colonial nature of the Nazi reconstruction efforts. Cumulatively, Groβmann makes the compelling argument that the transfer of radical occupation and destructive practices from East-to-West in the war's final phase was preceded by an earlier West-to-East transference.

Zwischen Fronten provides an intriguing examination of the militarization of the Franco-German frontier during the interwar period, its subsequent influence on military and political leaders’ prewar and wartime decision-making, as well as the consequences for the local populace. Groβmann leaves few stones unturned in this important transnational and comparative study. However, one area that warrants further consideration is the inspiratory role of previous sovereignty transfers. Nazi administrators inarguably introduced a heightened level of violence into their reordering of the borderland, but a striking element of the 1940 transition was the deliberate evoking of the post-1918 French Republican programmatic precedents as justification for their contemporary actions. Regardless of this observation, the monograph is a welcome addition to borderlands, nation-building, and Second World War historiography.