What did the U.S. do that resulted in it building and controlling the Panama Canal?
The US bought the rights to build a canal from the French (who tried and failed), and it backed a revolution against Colombia to create the nation of Panama.
The ability for shipping to transit through the Americas was a hope of politicians and businesspeople in all parts of the world (this was to save the weeks of travel and severe weather it would take to pass past Cape Horn (the southern most point of South America).
The US did three things to build and control the canal: it bought the rights to dig the canal from the French (France tried building it, banking on the success of having built the Suez Canal in Egypt, but inept management led to its failure), the US backed a revolution against Colombia that created the nation of Panama, and lastly Panama thanked the US for the help by granting control of the canal for US $10million.
A much fuller history of the Canal is here: