State responsibility — Nature and kinds of — For taking of, or interference with, property — Expropriation of shareholding — Situs of shares — Treaty requirement of prompt payment of just and effective compensation — Whether a clear and unambiguous standard — The law of the United States

States as international persons — In general — Recognition of acts of foreign States and governments — Act of State doctrine — Purpose and scope — Expropriation of property — Shares in Ethiopian company Held by Michigan corporation — Situs of shares — Whether shares located in Ethiopia — Exceptions to act of State doctrine — Existence of treaty imposing clear legal standards — Treaty of Amity and Economic Relations, 1951, between Ethiopia and United States — Requirement of prompt payment of just and effective compensation — Whether a clear and unambiguous standard — Hickenlooper Amendment — Whether applicable where expropriated property not brought to the United States — The law of the United States