He attended Colby College in Waterville but left school in 1862 to join the 20th Maine Volunteer Infantry Regiment as a captain.

[2] His official Medal of Honor citation reads: "Volunteered to attack the enemy's works in advance of orders and, upon permission being given, made a most gallant assault.

In Idaho and Washington, he managed Native American tribes and was commended by his superiors for his success in gathering the Indians on reservations and opening land for white settlers.

After being re-stationed in Fort Logan, Colorado, he led troops along the Cheyenne River in South Dakota during the Sioux uprising which followed the death of Sitting Bull.

[1] Appointed brigadier general on June 30, 1897, Merriam was transferred to the Department of the Columbia, which covered the northwestern United States.

At the outset of the Spanish–American War, he was named major general of volunteers and placed in command of the entire U.S. Pacific coast, including Hawaii.