Images of catastrophe and the suffering of others form an important part of the contemporary western imagination. Such images trace the geography of an uneven world at the same time as they assert the moral and political horizons of liberal forms of care towards it. Drawing upon Foucault's notion of political rationality, I revisit the emergence of this distinctively liberal moral geography to show how a modern form of ‘humanitarian reason’ (Fassin 2011) developed in concert with the rise of capitalism and the liberal state. In particular, I explore the processes that, during the course of the long 19th century, invoked both a market-driven moral economy and a state-driven political morality within humanitarian endeavour. The final part of the paper then applies these reflections on humanitarianism's past to its much-debated present. I move away from what is sometimes a rather binary focus on humanitarianism as a problem of Western intervention in other spaces to draw attention instead to its strategic function as a ‘liberal diagnostic’: a recursive moral practice that helps constitute a liberal politics as much as it projects that politics onto other people and places. I sketch out the implications of this by examining some of the ways that contemporary humanitarianism fulfils this role with respect to issues of global order and capital accumulation.