State immunity — Jurisdictional immunity — Whether presumption of sovereign immunity — Commercial activity exception — Distinction between sovereign and commercial acts — Distinction turning on nature, rather than purpose of act — Requirement of direct effect in United States — Foreign State under contractual obligation to make payment in the United States — Whether financial loss suffered as a result of non-payment constituting a direct effect — The United States Foreign Sovereign Immunities Act 1976 — Judgment in default — Grounds for setting aside judgment in default — The law of the United States