Final answer:
The Panama Canal, built by the US Army engineers in Panama, opened in 1914 and was transferred back to Panama on December 31, 1999.
Step-by-step explanation:
The US Army engineers built the Panama Canal in the country of Panama. Construction began in May 1904, with extensive work to build infrastructure, improve health conditions, and plan the engineering of the canal itself.
Dr. Walter Reed's work was vital in combating mosquito-borne diseases like malaria and yellow fever, significantly lowering the death rate and allowing progress on the canal to continue.
The Panama Canal was an extraordinary engineering achievement that drastically changed global trade and military defense patterns by creating a shortcut between the Atlantic and Pacific Oceans. The canal was completed in 1914 but was officially handed over to Panama on December 31, 1999.