The European Union (EU) and the antebellum US represent attempts to overcome anarchy without substituting hierarchy. Understood as ‘states unions’, these two systems are shown here to share foundational indeterminacy over sovereignty and the constitution of the people (i.e. the boundaries of the political community). Existing scholarship appreciates the EU's resulting democratic deficit but fails to problematize how dual ambiguity is sustained. The contrast between both states unions is used to probe this mutually constitutive relationship between sovereignty and democracy in an anti-hierarchical order. Defining the boundaries of the people by invoking popular sovereignty led in the antebellum, the paper argues, to a bifurcated debate over where the hierarchy of democratic legitimacy resided, destroying ambiguity. The contrast further shows that the EU has avoided the development of such rival, mutually exclusive constitutional visions that seek to make the people and sovereignty congruent at either the unit or union level. Instead, the EU has sustained dual constitutional ambiguity by allowing for multiple accountability claims reliant on overlapping notions of the people. Democratizing international cooperation thus should focus on the form democratic accountability can take rather than seeking to use popular sovereignty to establish some decision-making level where sovereignty and the people are congruent.