U.S. Practice of International Law: Background Information
Sean D. Murphy, United States Practice in International Law: (1999-2001) a thorough survey of U.S. international law practice arranged by topic, it includes citations to U.S. statutes, cases and documents, and international documents and materials.
Restatement of the Law, Third, Foreign Relations (1987), this unofficial but authoritative digest is also available on Westlaw (REST-FOREL) and LexisNexis (INTLAW;FORREL).
A good source for historical information is Charles Cheney Hyde’s International Law Chiefly as Interpreted and Applied by the United States (2d. rev. ed., 1947), a three-volume set that examines U.S. views on international law up to 1941.