With the outbreak of the American Civil War in 1861, Clark, who was wealthy and owned 160 slaves, became a leading secessionist in Missouri. After the pro-secessionist Missouri State Guard (MSG) was formed in May 1861, Clark was appointed by Jackson to be a brigadier general commanding the MSG's 3rd Division.
Clark, a wealthy man with 160 slaves, became a prominent secessionist in Missouri during the American Civil War. Following the formation of the pro-secessionist Missouri State Guard (MSG) in May 1861, Clark was appointed by Jackson to command the MSG's 3rd Division.