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.
Hay–Bunau-Varilla Treaty
This treaty was a source of conflict between Panama and the United States since its creation. The Canal Zone became a racially and socially segregated area, set aside from the country of Panama. The push for environmental determinism seemed to be the best framework to justify American practices in Panama. The conflict from the treaty reached its peak on January 9, 1964, with riots over sovereignty of the Panama Canal Zone. The riot started after a Panamanian flag was torn during conflict between Panamanian students and Canal Zone Police officers, over the right of the Panamanian flag to be flown alongside the U.S. flag. U.S. Army units became involved in suppressing the violence after the Canal Zone Police were overwhelmed. After three days of fighting, about 22 Panamanians and four U.S. soldiers were killed. This day is known in Panama as Martyrs' Day.