The gang became notorious for taking scalps under highly questionable circumstances to claim the bounties, and its members were eventually declared outlaws by the Mexican government.

[3]: 299 During the American Civil War, after being chief of staff to Brigadier General William W. Averell and Lieutenant Colonel of the 1st Massachusetts Cavalry Regiment, Chamberlain commanded Camp Parole at Annapolis, Maryland, for a time and also commanded the 5th Massachusetts Colored Cavalry, an all African-American unit, with the rank of colonel.

He was wounded on six occasions during the war,[4]: 169  including on March 17, 1863, at Kelly's Ford, Virginia, when a Confederate bullet hit his left cheekbone.

[3]: 301  Settling in Massachusetts with his family, Chamberlain became well known for his charming paintings, which consist largely of landscapes and battle scenes depicting the Mexican–American War.

[6] Chamberlain also authored and illustrated a harrowing autobiographical account of his travels during the 1840s, especially his service in the Mexican–American War and his adventures with the Glanton gang, entitled My Confession: The Recollections of a Rogue, which he wrote between 1855 and 1861.

[7] The account also informed the narrative and characters of author Cormac McCarthy's 1985 novel Blood Meridian;[8]: 1  the novel's protagonist, known only as "the kid", is said to be loosely based on Chamberlain.