Union Army of the West
On June 13, 1861, after failed negotiations with Governor Jackson, Lyon quickly moved his army to attack the pro-confederate forces at Jefferson City, Missouri. the state capital. He moved quickly enough to catch them unprepared. On June 15, the Army of the West occupied Jefferson City. On June 17, both sides fought the Battle of Boonville which lasted only about 30 minutes. The Union forces completely routed the pro-confederates. Jackson and most of his militia retreated to the southwest corner of Missouri, close to Confederate help from Arkansas.