[5] He was also the great grandson of Aaron Root, a Lieutenant Colonel of the First Berkshire County Regiment of the Massachusetts militia.

[6] When the American Civil War began Pierce was captain of a militia company, the Valley City Lights Guard, before entering Federal service in June 1861[5] and was appointed captain[1] He then served as a company commander in the 3rd Michigan Infantry Regiment at the Battle of First Manassas.

[1] Pierce continued to serve as part of the Army of the Potomac during the Peninsula and Seven Days campaigns, rising the ranks.

[1] Pierce's regiment also fought Confederate forces, led by Joseph B. Kershaw, in the defense of the Peach Orchard during the second day of the Battle of Gettysburg.

[1][6] Overall, Pierce was wounded five times during the war and was present in all of the major battles in the East from First Bull Run to Appomattox.

[11][12] After the war he was active in veteran affairs, serving as the Grand Army of the Republic's commander of the Department of Michigan for two years.