The environment has traditionally been a marginal concern in international relations, but the climate crisis has highlighted the importance of the relationship between society and the natural world. In The ideal river, Joanne Yao offers a remarkable account of how nineteenth-century efforts to tame nature shaped our modern international order. Examining historic attempts to establish international commissions on three transboundary rivers – the Rhine, the Danube and the Congo – she reveals how the Enlightenment ambition to master the natural world has informed our geographical imagination of the international. This idea of domination over nature shaped three concepts central to the emergence of early international order: the territorial sovereign state, imperial hierarchies and international organisations. As The ideal river shows, the relationship between society and nature is at the heart of international politics.