National Geographic: For nearly a century the Panama Canal has been the only game in town for anyone who wanted to sail from the Atlantic to the Pacific without making the long voyage around Cape Horn. In that time more than a million ships, from bulk carriers to cruise liners to nuclear submarines, have passed through its locks, taking advantage of the world's most famous shortcut. Panama's canal may (or may not) soon face stiff competition. Last June Nicaragua's National Assembly overwhelmingly approved a plan to...