In "The Man Without a Country," what is Philip Nolan guilty of? Why was he a man without a country?

Edward Everett Hale's "The Man Without a Country" is based on the true story of Philip Nolan, an American army officer who becomes connected with the trial of Vice President Aaron Burr. Burr was being tried for treason, and Nolan was charged as a co-conspirator. While on the witness stand, Nolan cursed the United States, and the judge later sentenced Nolan to serving a life imprisonment without ever again setting foot on U.S. soil or hearing the name of his country mentioned again. Nolan served out the remainder of his sentence on board U.S. Naval ships--never setting foot on lan again. He eventually repented after reading Sir Walter Scott's Lay of the Last Minstrel, particularly the line "Breathes there the man with soul so dead / Who never to himself hath said / "This is my own, my native land!" Late in life, Nolan was told of the might of his nation, and he died a proud and happy man. He also served heroically during a British attack on his ship, taking control of a gun after the officer in charge was killed.