Is the Panama Canal American territory?
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Colombia, France, and later the United States controlled the territory surrounding the canal during construction. The US continued to control the canal and surrounding Panama Canal Zone until the 1977 Torrijos–Carter Treaties provided for handover to Panama. After a period of joint American–Panamanian control, in 1999, the canal was taken over by the Panamanian government. It is now managed and operated by the government-owned Panama Canal Authority.
Panama Canal
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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.
History of the Panama Canal
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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.
United States territorial acquisitions
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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 Canal Zone
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The small Panama Canal Zone was United States territory, and American forces from the U.S. Navy, U.S. Army, the USAAF (at Howard Air Force Base), and Colombian forces helped inside the Canal Zone, guarded the Panama Canal from both ends. This Canal provided the United States and its Allies with the ability to move warships and troops rapidly between the Atlantic Ocean and the Pacific Ocean. Since most of the American shipbuilding capability was on the East Coast and the Gulf of Mexico, the Canal was vital for moving new warships to the Pacific to fight the Imperial Japanese Navy
World War II by country
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The history of Panama during World War II begins in 1939. Due to the American-controlled Panama Canal cutting across the center of the country, Panama was of major strategic importance to the Allied war effort, as well as the most important strategic location in Latin America during World War II. It provided an invaluable link between the Atlantic and Pacific Oceans that was vital to both commerce and the defense of the Western Hemisphere. Therefore, the defense of the Canal Zone was the United States' chief concern in the American Theater. Panama never received Lend-Lease assistance, but in return for the rights to build military infrastructure within Panamanian territory, the United States undertook large-scale public works projects, which did much to modernize the country and boost the economy.
Panama during World War II
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The evolution of the relation between Panama and the USA has followed the pattern of a Panamanian project for the recovering of the territory of the Canal of Panama, a project which became public after the events of May 21, 1958, November 3, 1959, and then on January 9, 1964. The latter day is known in Panama as the Martyrs' Day (Panama), in which a riot over the right to raise the Panamanian flag in an American school became the vicinity of the Panama Canal.
Panama–United States relations
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The U.S. Postal Department also used general issue stamps with the territorial name overprinted, such as PUERTO RICO, CUBA, GUAM, PHILIPPINES or CANAL ZONE. Cuba was granted independence, Canal Zone returned to Panama. 
Alternatively, the U.S. issued a 1932 'United States of America' stamp for 18 centavos in the Philippines, 1930 stamps for use in Guam only designated 'Guam Guard Mail, or 1952 'Ryukyus' stamp for 100 yen in Okinawa. The Philippines was granted independence, the Ryukyus were returned to Japan. 
Panama Canal has been featured on several U. S. commemorative stamps, as well as on Panama's own postage. The territory was returned to Panama.
Territories of the United States on stamps
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Effective July 1, 1951, under an act of Congress dated September 26, 1950 (64 Stat. 1038), governance of the Canal Zone was through the Canal Zone Government with the canal operated by the Panama Canal Company until 1979 when the Panama Canal Commission took over its governance. The entire structure was under the control of the United States government with the Secretary of the Army appointing the Panama Canal Company board of directors and the Canal Zone Government was entirely financed by the company. The office of Governor of the Panama Canal Zone was not usually a stepping stone to higher political office but a position given to a US Army active duty general officers of the United States Army Corps of Engineers. The Governor was also President of the Panama Canal Company. The Canal Zone had its own police force (the Canal Zone Police), courts, and judges (the United States District Court for the Canal Zone). Despite being an unincorporated territory, the Canal Zone was never granted a congressional delegate.
Panama Canal Zone
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Following the United States' acquisition of Alta California in 1846 and the Oregon Territory in 1848, following the Mexican–American War and with the prospective movement of many more settlers to and from the West Coast, the United States again turned its attention to securing a safe, reliable, and speedy link between the Atlantic and Pacific oceans. In 1846 the United States signed a treaty with Colombia (then the Republic of New Granada) by which the United States guaranteed Colombian sovereignty over Panama and was authorized to build a railroad or canal at the Panamanian isthmus, guaranteeing its open transit.
Panama Canal Railway