State responsibility — Nature and kinds of — For revocation of, or interference with, concessions or concessionary contracts — Nature of rights under oil concession — Whether contractual or proprietary — Title to oil prior to extraction — Governing law — Whether nationalization of concession is an expropriation of oil yet to be extracted — Act of State doctrine — Hickenlooper Amendment — The law of the United States

States as international persons — In general — Recognition of acts of foreign States and governments — Act of State doctrine — Nationalization of oil concession — Whether Hickenlooper Amendment applicable — Requirement that plaintiff claim title or assert a property right — Rights under oil concession — Whether contractual or proprietary — Whether concession holder possessing title to oil yet to be extracted — Views of the State Department — The law of the United States