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. Lyon installed a pro-Union government after Jackson and most of his militia retreated to the southwest corner of Missouri. Lyon moved his army to go after the rebels. On June 17, both sides fought the Battle of Boonville which lasted only about 30 minutes. The Union forces completely routed the pro-confederates. He then lead his troops into a series of skirmishes with the Missouri State Guard and the Confederate Army.