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 1977 Panama Canal Treaties entered into force on October 1, 1979. They replaced the 1903 Hay–Bunau-Varilla Treaty between the United States and Panama (modified in 1936 and 1955), and all other U.S.-Panama agreements concerning the Panama Canal, which were in force on that date. The treaties comprise a basic treaty governing the operation and defense of the Canal from October 1, 1979 to December 31, 1999 (Panama Canal Treaty) and a treaty guaranteeing the permanent neutrality of the Canal (Neutrality Treaty).