Union Army of the West
By the time the Civil War started, Missouri had already already been engaged in a border war between free-soilers and proslavery forces over statehood for neighboring Kansas. Both parties raided both sides of the border. There was a great deal of lawlessness and panic in the region. When the Civil War started, the issue became whether Missouri would join the Confederacy or remain loyal to the Union. The newly elected governor in 1860 was Claiborne Fox Jackson. While he openly did not call for secession from the Union, he was making plans for Missouri to join the Confederacy. He knew the most important resource in the state was the federal arsenal at St. Louis. There was only a small detachment of Union soldiers that guarded the arsenal and were under the command of Captain Lyon. Jackson called out his state militia.