United States territorial acquisitions
The Panama Canal Zone was an unorganized US territory located within the Republic of Panama. It was established under the Hay–Bunau-Varilla Treaty in 1903 and disestablished in 1979 under the Torrijos–Carter Treaties. Panama gained full control over the Panama Canal in 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.