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.
Panama–United States relations
The United States first attempted to acquire control of a canal on the Panamanian isthmus via the Hay-Herran Treaty of 1903, but the treaty was not ratified. Desperate to construct a canal, the United States saw the separatist movement as an opportunity. Despite the Bidlack-Mallarino Treaty of 1846 in which the United States would intervene in the event of a disorder between Panama and Colombia in Colombia’s favor, the United States prevented Colombian forces from moving across the isthmus to stop the Panamanian uprising. On November 4, 1903, the immediate support of the USA secured the Declaration of Independence of Panama from Colombia. In return, Panama signed the Hay–Bunau-Varilla Treaty three weeks later, granting the USA sovereign rights over the interoceanic canal that would be built over the following decade.