- Camp Jackson Affair (May 10, 1861)
- Harney-Price Agreement (May 21, 1861)
- Planter's House Meeting (June 11, 1861)
Although far away from the Missouri-Kansas border, events in and around St. Louis in early 1861 altered the course of the war for western Missouri. Concerned that the secessionist Governor Claiborne Fox Jackson would seize the federal arsenal at St. Louis, Captain Nathaniel Lyon, commander of the arsenal, recruited a paramilitary unit known as the St. Louis Wide Awakes, which could muster into the federal army with the beginning of war. Meanwhile, Governor Jackson stationed members of the Missouri State Guard outside the city at Camp Jackson. On May 10, 1861, Lyon led his men to Camp Jackson and secured its surrender, but as he marched the prisoners through St. Louis, protesters heckled Lyon's new recruits, who opened fire on the civilians, killing more than 20 of them. The incident soon became known as the Camp Jackson Affair, and meetings on May 21 and June 11 failed to reach a lasting peace between the Missouri's Union and secessionist leaders. Missouri officially stayed in the Union, and Governor Jackson was exiled, but ongoing regular and guerrilla warfare ensured that the state's status remained unsettled throughout much of the war. St. Louis, meanwhile, remained in Union hands and served as an important industrial and military site on the Mississippi River.