A state of the Union may preserve its immunity from suit in its own courts, and the Constitution restricts its amenability to suit in the federal courts. Yet in Nevada v. Hall the Supreme Court held that in a motor-vehicle accident case a state cannot claim a constitutional immunity from suit in the courts of a sister state. The Court indicated, however, that if a suit involved a defendant state's “capacity to fulfill its own sovereign responsibilities,” different constitutional considerations might control. In vigorous dissents Justices Blackmun and Rehnquist argued that the reasoning of the majority precluded even this possibility. Justice Rehnquist suggested that in making such distinctions in the future, the Court would be “truly adrift on uncharted waters.” It may be, however, that there already is a chart to these waters, discoverable from the majority's reasoning though not obvious from the opinion. That chart is the international law of sovereign immunity.
John M. Rogers, Applying the International Law of Sovereign Immunity to the States of the Union, 1981 Duke L.J. 449 (1981).