History of the Panama Canal
During World War II, the canal proved a vital part of the U.S. military strategy, allowing ships to transfer easily between the Atlantic and Pacific. Politically, the Canal remained a territory of the United States until 1977, when the Torrijos–Carter Treaties began the process of transferring territorial control of the Panama Canal Zone to Panama, a process completed on 31 December 1999.
Hay–Bunau-Varilla Treaty
The Republic of Panama grants the United States with the use of the land said canal be built, the surrounding land for construction purposes, and all islands within the limits of the zone