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)
The Republic of Panama became a de facto protectorate of the larger country through two provisions whereby the United States guaranteed the independence of Panama and received in return the right to intervene in Panama's domestic affairs. For the rights it obtained, the United States was to pay the sum of US$10 million and an annuity, beginning 9 years after ratification, of US$250,000 in gold coin. The United States also purchased the rights and properties of the French canal company for US $40 million.