From its creation during the Wars of Unification (1864-71) until its defeat at the end of the First World War, the German army remained a federal institution. To be sure, the imperial constitution recognized the Kaiser as commander-in-chief of Germany's land forces. Under the Kaiser's direction, the Prussian war ministry prepared the military budget and the Prussian General Staff drafted operational plans for future wars. A patchwork of military agreements nevertheless limited the authority of the Kaiser and Prussia's military leaders over nearly one-quarter of the German army. According to these agreements, separate war ministries, cadet schools, and general staffs oversaw the arming, clothing, feeding, housing, and training of Bavarians, Saxons, and Württembergers, while the monarchs of Germany's three smaller kingdoms determined personnel appointments, the deployment of units, and even the design of insignia and uniforms. The army's contingent-based structure ensured that Prussians and non-Prussians served alongside, but only rarely with, one another after 1871. Based on research in archives and libraries in Germany, Austria, England, and the United States, this dissertation explores the means by which the smaller armies of Bavaria, Saxony, and Württemberg were integrated into Prussia's much larger military structure after 1871 and seeks to understand why the German army, burdened by numerous loyalties and overlapping spheres of control, did not simply fall apart during the First World War. It argues that even though the decentralization of military authority and the presence of dual loyalties among Bavarian, Saxon, and Württemberg soldiers remained serious concerns for Prussian authorities, the German army proved remarkably durable because the empire's monarchs and their advisors preferred compromise, rather than conflict, with one another. This dissertation contributes to ongoing historiographical debates concerning the process of nation-building and the consolidation of state power across Europe since the French Revolution; the evolution of the relationship between monarchs and their militaries in a period characterized by public opinion shaped by parliamentary debates and a mass press; and the ability of multiethnic and multinational empires to mobilize their diverse societies for war at the turn of the twentieth century and on the eve of two global conflicts.