He served as brigade commander for much of the war but his highest actual substantive grade was colonel.

[1][2] Root enlisted in the Union Army at the beginning of the war and, on May 20, 1861, he was appointed lieutenant colonel of the 21st New York Volunteer Infantry, nicknamed the "1st Buffalo Regiment" because it was the first regiment mustered into the Union Army from Buffalo, New York.

[4] After the close of hostilities, from May 13, 1865, to June 23, 1865, Root commanded the 3rd Brigade, 3rd Division, V Corps of the Army of the Potomac.

[1] On January 13, 1866, President Andrew Johnson nominated Root for appointment to the grade of brevet major general of volunteers, for faithful and meritorious service during the war, to rank from March 13, 1865, and the U. S. Senate confirmed the appointment on March 12, 1866.

[2][5] After the war, Root was a warehouse executive and newspaper editor at Buffalo, New York.