Panama Canal Zone
The Panama Canal Zone () was an unincorporated territory of the United States from 1903 to 1979, centered on the Panama Canal and surrounded by the Republic of Panama. The zone consisted of the canal and an area generally extending on each side of the centerline, excluding Panama City and Colón, which otherwise would have been partly within the limits of the Zone. Its border spanned three of Panama's provinces. When reservoirs were created to assure a steady supply of water for the locks, those lakes were included within the Zone.
History of Panama (1821–1903)
Throughout the period of turmoil, the United States had retained its interest in building a canal through either Nicaragua or Panama. An obstacle to this goal was overcome in December 1901 when the United States and Britain signed the Hay–Pauncefote Treaty. This treaty nullified the provisions of the Clayton–Bulwer Treaty of 1850 and signified British acceptance of a canal constructed solely by or under the auspices of the United States with guarantees of neutrality.