Between 1914 and 1921, Adelaide Rosalia Hasse compiled a three-volume Index to United States Documents Relating to Foreign Affairs, 1828-1861, available online in full text via the Hathi Trust.
U.S. foreign relations materials in the pre-1861 U.S. Congressional Serial Set: A much shorter index of the foreign affairs material in the Serial Set, compiled by the Office of the Historian.
FSU Library Databases
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Department of State Telegrams
Public Papers of the Presidents of the United States
Association of Southeast Asian Nations