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.
History of Panama (1821–1903)
Furthermore, the United States was entitled to acquire additional areas of land or water necessary for canal operations and held the option of exercising eminent domain in Panama City. Within this territory Washington gained "all the rights, power, and authority . . . which the United States would possess and exercise if it were the sovereign ... to the entire exclusion" of Panama.