Historical research on the German army of the interwar period has concentrated on the development of the so-called ‘Blitzkrieg’. However, Matthias Strohn shows that for most of the time the German army, restricted by the terms of the Versailles Treaty, was too weak to launch an offensive war or even effectively repel an invader. Accordingly, the army focused instead primarily on planning a defensive war against superior enemies, especially France and Poland. Making extensive use of German archival sources, Strohn explores the development of military thought and doctrine for the defence of Germany and shows how these ideas were tested in war games and staff rides. His findings comprehensively revise our understanding of the German army in this period, shedding new light on the ideas of leading figures in the German military and how events, such as the occupation of the Ruhr in 1923, influenced military planning.