State immunity — Jurisdictional immunity — Individual acting in official capacity on behalf of government instrumentality — Whether entitled to sovereign immunity — Official acting for personal motives — Whether acting in official capacity — Tort exception — Whether instruction to bank to halt payment of letter of credit constituting tortious act — Expropriation exception — Requirement that expropriation be in violation of international law — Waiver — Co-defendants that are unrelated instrumentalities of the same State — Whether waiver by one co-defendant constituting implied waiver by other co-defendant — United States Foreign Sovereign Immunities Act 1976 — The law of the United States