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.
Postage stamps and postal history of the Canal Zone
The Republic of Panama was formally part of Colombia, and after it broke away from Colombia, with assistance from the United States, it established itself as a separate nation where it immediately became necessary to establish its own post offices and issue its own postage stamps. The Canal Zone Post Office was inaugurated on June 25, 1904. Beforehand the domestic rates of postage in the United States were made applicable to all possessions of the United States on June 20, 1904, which henceforth included the Canal Zone.