Foreign Relations of the United States

Overview
Foreign Relations of the United States (FRUS) is the official documentary historical record of major U.S. foreign policy decisions and significant diplomatic activity. The series, which is produced by the State Department’s Office of the Historian, began in 1861 and now comprises more than 350 individual volumes. The volumes published since 1980 increasingly contain declassified records from all the foreign affairs agencies.

Source
U.S. Department of State, Office of the Historian.