By 1848, the British Foreign Office explicitly instructed consuls in Southern states to lobby state lawmakers to liberalize the Seamen Acts, thereby replacing lawsuits and federal diplomacy. The Foreign Office’s shift paid dividends, with several states removing mandatory incarceration from their Seamen Acts. However, the move to state-level diplomacy formalized Britain’s abandonment of black citizenship in its fight against the Seamen Acts. While state-level diplomacy resulted in the end of incarceration and physical violence against itinerant free black seamen, the sailors were treated as objects of law and politics, not legal subjects endowed with enforceable rights. This diplomatic surrender both foreshadowed and complemented American constitutional change. When the US Supreme Court decided Dred Scott, it moved ever closer to canonizing substantive rights and national citizenship – appropriating the discourse of the Seamen Acts opponents – but only as it simultaneously denied black citizenship. The once-diverging trajectories of the United States and Great Britain regarding black citizenship converged again; citizenship was a white prerogative.