Increasing alarm over global environmental challenges has elevated society's relationship with the natural world into the theoretical limelight. Engagement with environmental politics, however, has largely paid less attention to how the eighteenth- and nineteenth-century quest to tame nature shaped the modern international order. The ideal river examines nineteenth-century efforts to establish international commissions on three transboundary rivers - the Rhine, the Danube, and the Congo, and how the Enlightenment ambition to tame the natural world, informed our geographical imagination of the international. This relationship of domination over nature shaped three core concepts central to the emergence of early international order: the territorial sovereign state; imperial hierarchies; and international organizations. The book highlights how the relationship between society and nature is not a peripheral concern, but one at the heart of international politics.