"President James Madison named John Armstrong to his cabinet as Secretary of War on June 14, 1813. Armstrong had served as minister to France but the appointment was really an attempt by Madison to build political alliances. Armstrong was a force in New York politics, and with so much military action taking place along the border with Canada, Madison needed the state firmly in his camp. Unfortunately, Armstrong proved to be a disastrous choice due to his political and personal shortcomings."
Armstrong’s chief qualities were described by at least one acquaintance as “obstinancy and self-conceit.”
Armstrong was the author of a book published in 1814 entitled “Hints to Young Generals.” Although he had no real military experience, this popular book established Armstrong as an expert at a time when the United States were desperate for military officers.
From History of the United States of America under the Constitution, Volume 2 :
See a portrait of John Armstrong here.