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 Zone
Through the remainder of the 19th century, the United States landed troops several times to preserve the railway connection. At the same time, it pursued a canal treaty with Colombia (as New Granada was renamed). One treaty, signed in 1868, was rejected by the Colombian Senate, which hoped for better terms from the incoming Grant administration. Under this treaty, the canal would have been in the middle of a 20-mile zone, under American management but Colombian sovereignty, and the canal would revert to Colombia in 99 years. The Grant administration did little to pursue a treaty and, in 1878, the concession to build the canal fell to a French firm. The French efforts eventually failed, but with Panama apparently unavailable, the United States considered possible canal sites in Mexico and Nicaragua.