He is best known for his effective and brutal acts as the leader of a successful militia campaign from 1868 to 1869 against Ku Klux Klan chapters in the state.
He left the army in 1865 at the end of the war and opened a building material business in New York City.
His success, however, fueled resentment by the ex-Confederate populace, who considered him a Northern carpetbagger thriving off the South's defeat and impoverishment.
The amendment was ratified, but the violence prompted Governor Clayton to form state and local militias to combat the Klan insurgency.
This quickly made him a marked man, and on October 2, 1868, after numerous threats and reported Klan surveillance of his home, Upham and Woodruff County registrar F.A.
In early November 1868, Governor Clayton cancelled all elections and declared martial law, splitting the state into four military districts.
Upham gave his men a free hand in subduing the Klan, and the militia's war against them was bloody and ruthless.
There is no other way ... nothing but good, healthy, square, honest killing would ever do them any good.Enraged by his tactics, a force of about 30 Klansmen rode to Upham's hometown of Augusta and attempted to take over the town.
However, upon learning that 300–400 Klan reinforcements were on their way, the militia tore through Augusta, beating and arresting suspected Klansmen.
A fierce battle erupted on Upham's property, which ended in a crushing and demoralizing defeat for the Klan.
In May 1873, Republican governor Elisha Baxter dismissed him from the Arkansas State Militia, along with other men with ties to Powell Clayton, in an attempt to win over ex-Confederates.
In the History Channel TV documentary Aftershock: Beyond the Civil War, Upham is featured prominently, portrayed by Brian Danner.