In federal Indian law, preemption is about preempting colonialism. This may seem strange; preemption classically blocks the authority of non-federal sovereigns. In Indian affairs, however, preempting state law creates room for Indigenous sovereignty, allowing tribal governments to shape the social, economic, and cultural conditions for their communities to thrive. In so doing, it limits the ravages of colonial domination by restoring some of the autonomy and well-being that colonialism took away.

But federal Indian affairs preemption is at risk. It is threatened both by the Supreme Court’s offhand comments in Oklahoma v. Castro-Huerta and by the failure of past decisions to coherently describe the doctrine. This Article addresses this threat. It first shows how constitutional and structural differences explain variations in preemption in other fields, and then reveals the constitutional and structural roots of modern federal Indian law preemption. In so doing, it gives cohesion to past precedent and ensures the vitality of this bulwark against colonial domination.