|Born in Pennsylvania in 1758,
Armstrong attended the College of New Jersey (Princeton) but did not graduate.
He volunteered instead to fight in the American Revolutionary War before
completing his studies. He fought at Trenton and Princeton, and served as
an aide to Horatio Gates. After the Revolution, Armstrong was briefly involved
in Pennsylvanian politics, and served in the Senate before going to France
as U.S. minister from 1803 to 1810.
At the outbreak of the War of 1812 , Armstrong was commissioned Brigadier General and charged with the defense of New York City. Later that year, when William Eustis was forced to resign as secretary of war, President Madison named Armstrong to replace him, though Secretary of State Monroe and Secretary of the Treasury Gallatin strongly opposed the appointment.
Armstrong oversaw the formulation of the "Rules and Regulations of the Army of the United States", which became the model for all future editions. One of Armstrong's primary concerns was economic. To save money, he encouraged officers to avoid the use of militia whenever possible. He also believed that it was the secretary's duty to direct officers in the field to ensure implementation of government policies. This quickly soured his relations with most of his generals, who naturally resented Armstrong's habit of sending orders directly to their subordinates. Armstrong's habitual disregard for the formal chain of command eventually brought about the resignation of Major General William Henry Harrison. When Armstrong replaced Harrison with militia general Andrew Jackson without seeking presidential approval, President Madison formally reprimanded him and outlined specific guidelines for all future appointments.
Armstrong had long been accused of neglecting the defense of the capital, but when the British sailed into Chesapeake Bay in the summer of 1814, criticism of him reached new heights. Over Armstrong's objections, President Madison appointed William Winder to oversee the defense of Washington. Winder wanted to mobilize the militia right away, but Armstrong refused to allow it on account of his theory that the militia fought best at the spur of the moment. When the British reached Benedict on August 19, Armstrong got the chance to see his militia battle-theories tested.
The subsequent American defeat at Bladensburg, closely followed by the burning of Washington, were not entirely Armstrong's fault. Secretary of State Monroe, among others, had interfered with the effective placement of the troops. Popular sentiment blamed Armstrong and he was soon forced to resign. He retired from public life to manage his extensive New York estates. He died in 1843.