Against both liberal narratives and postcolonial critiques, this article argues that sovereignty-as-responsibility – the theory of sovereignty embraced in the responsibility to protect (R2P) – is part of a problem space that emerged with decolonization, rather than the end of the Cold War. The internally displaced person (IDP), the vehicle which Francis Deng used to critique Westphalian sovereignty, had to be theorized against the rise of the postcolonial state. In recovering the questions motivating Deng, we find a stark politics driving his work on IDPs and sovereignty. Against the claim that the heart of R2P is armed coercive intervention for humanitarian purposes, Deng used sovereignty-as-responsibility to promote a profoundly political critique of the colonial legacy and the postcolonial state, which was taken up by states of the Global South in debates on the ratification of R2P. Recovering Deng's work on IDPs and sovereignty-as-responsibility highlights R2P as itself a site of contestation, and offers a case for how ideas emerge ‘from below’ in global politics.