After the beginning of the Civil War, the arsenal in Liberty, MO had been attacked by pro-Confederates and a large number of rifles and muskets were taken. The arsenal in St. Louis was by far much larger than the one in Liberty, with as much as 40,000 rifles and muskets. Fears that the pro-Confederates would attempt to seize the St Louis arsenal, a militia was raised under the command of Captain Nathaniel Lyon to protect the arsenal. Lyons militia was largely composed of German immigrants and members of the Wide Awakes organization.

Governor Claiborne Fox Jackson ordered the Missouri Militia for maneuvers just outside of the arsenal in what was known as Camp Jackson. The governor at this point was considered neutral, but had strong leanings towards the South.

On May 10, 1861, Lyons would force the surrender of the militia, but the men refused to take the oath of allegiance and Lyons marched the men to the arsenal through the streets of St Louis, guarding them with members of the German Home Guard. This sparked outrage with the citizens and they began to hurl rocks and pavement at the Union soldiers, particularly aiming at the Germans. A shot was fired and then Germans opened fire into the crowd, killing at least 20 civilians and wounding at least 50 more.

Rioting ensued and many more citizens and soldiers were beaten and mistreated. Eventually, Federal regular Army troops arrived and martial law was enacted. The relief of the Germans however, abated the situation and the rioting ended.

The Camp Jackson Affair would be an event that further provided proof of division in the country, and in the state of Missouri. It would also be one of the deciding factors in forcing most Missourian’s to pick a side as issues of the day such as nativism, slavery, and state’s rights were now thrust upon them. It would also be the catalyst in Lyons promotion to Brigadier General and replacing General William S. Harney as commander of Union forces in Missouri and for solidifying Governor Claiborne Jackson’s and former governor Sterling Price’s pro-Confederate position.

Price, Jackson, Lyons and Frank P. Blair Jr. would meet at the Planter House Hotel in St Louis to try and come to terms with the situations in Missouri, but Lyons would basically declare war and would then begin his pursuit of the pro-Confederates across the state, sparking many of the battles that would dot the countryside.