In 2005, the United Nations reinterpreted its charter to facilitate humanitarian intervention, defining military action to prevent serious human rights abuses as a legitimate means of maintaining international peace and security. Under circumstances of ‘genocide, ethnic cleansing and other such crimes against humanity’, states have a ‘responsibility to protect’ the victims and, if required, to use military means to do so. This new state responsibility is a response to new asymmetries in the exercise of sovereign power worldwide. In theory, it imposes new conditions on the exercise of state sovereignty that extend the principle of collective security beyond states to include all people. In practice, it gives those with the capacity to intervene, namely the dominant powers, the responsibility to intervene in the affairs of weaker ‘failing’ states. In this article, I use official texts to explore this new humanitarian collective security. Drawing on a range of accounts, including the Australian experience of intervention in East Timor, I argue that the grounds for humanitarian intervention lie as much in the defence of order as in the pursuit of justice. Dominant states assert their shared vulnerability and justify intervention as pre-empting presumed threats; they thus recruit humanitarianism for state security. Humanitarianism, however, is not so easily contained. As military practice collides with normative rhetoric, deep contradictions emerge between order and justice. Normative claims implode and spill over, feeding alternative humanitarianisms founded on mutuality and solidarity. The disordering order–justice dialectic can thereby prefigure reorderings beyond hegemonism.