History of the Panama Canal
During World War II, the canal proved a vital part of the U.S. military strategy, allowing ships to transfer easily between the Atlantic and Pacific. Politically, the Canal remained a territory of the United States until 1977, when the Torrijos–Carter Treaties began the process of transferring territorial control of the Panama Canal Zone to Panama, a process completed on 31 December 1999.
United States territory
From July 8, 1947, until October 1, 1994, the United States administered the Trust Territory of the Pacific Islands, but the Trust ceased to exist when the last member state of Palau gained its independence to become the Republic of Palau. The Panama canal, and the Canal Zone surrounding it, was territory administered by the United States until 1999, when control was relinquished to Panama.