In addition to "Twenty Thousand Leagues Under the Sea", he wrote an 1887 story on the Civil War, "North Against South"
In 
1889 Verne wrote a second sequel to the novel, The Purchase of the North Pole 
.... Conqueror (1886) * North Against South (1887) * The Flight to France (1887) * 
Two... [DOC] [TLE] Verne's Best Friend and his Worst Enemy: I.O.