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.
Panama Canal Railway
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.