Most constitutional law scholars pay no attention to the field of conflicts of law. Conflicts governs the law of multi-jurisdictional litigation—like which state’s law to apply when a railroad worker is injured on a train from Alabama to Mississippi, or whether a marriage in one state will be recognized in another, or how to enforce a court’s ruling against assets or people in another state. And as those examples might suggest, it can frequently seem like a technical adjunct to civil procedure.
Yet conflicts questions frequently do interact with constitutional law principles of federalism. One example is the doctrine of “extraterritoriality”—the limits on a state’s ability to regulate stuff that takes place somewhere else. Territoriality is a basic premise of the federal system; everybody knows that the New York legislature can’t just sit down and rewrite all of the laws of New Jersey. This seems like a common-sense requirement of our constitutional structure. But as Clyde Spillenger demonstrates in Risk Regulation, Extraterritoriality, and the Constitutionalization of Choice of Law, 1865-1940, the nature and source of this principle is misunderstood today.