[3] During the American Civil War, Jenkins served in the Union Army under Generals Grant, Pope, Sherman and Burnside in the Western Theater.

Jenkins saw his first combat action in two engagements near Lexington, Missouri, and helped negotiate the surrender of Federal forces in that vicinity to the Confederates in September 1861, becoming a prisoner of war.

His daughter, Emma Rue, donated the eastern edge of their homestead to the city for the Coliseum (now the Spokane Veterans Memorial Arena).

Jenkins, a strong supporter of education, attempted twice to fund the first university in Spokane, which ultimately failed due to the economic Panic of 1893.

The colonel was also concerned about young men who had to forego higher education to work to support themselves and their families, so he created a trust of $50,000 to fund Spokane's first vocational school for adults, located in and directed by the YMCA.