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)
Naval operations during the Spanish–American War (1898–1901) served to convince U.S. President Theodore Roosevelt that the United States needed to control a canal somewhere in the Western Hemisphere. This interest culminated in the Spooner Bill of June 29, 1902, providing for a canal through the isthmus of Panama, and the Hay–Herrán Treaty of January 22, 1903, under which Colombia gave consent to such a project in the form of a 100-year lease on an area 10 kilometers wide. This treaty, however, was not ratified in Bogotá, and the United States, determined to construct a canal across the isthmus, intensively encouraged the Panamanian separatist movement.