Heirs of German Jewish art dealers alleged that the Nazi government coerced their family consortium into selling the Welfenschatz, a collection of medieval relics, for a fraction of its value. After Germany and a German museum instrumentality invoked immunity under the Foreign Sovereign Immunities Act, the heirs relied on the Act’s exception for property taken in violation of international law. The Supreme Court held that this phrase refers to the international law of expropriation and incorporates the domestic-takings rule. A sovereign’s taking of its own nationals’ property generally does not violate that body of international law. The Court did not resolve an alternative argument that the consortium members were not German nationals when the sale occurred. It vacated the judgment of the Court of Appeals and remanded for that court to direct the district court to consider the preserved status of that alternative argument.