I spoke about this topic at the recent meeting of the Northern Plains Civil War Round Table to a small audience, but it was fun.
May 10, 1861 represented a day of conflict and violence on the streets of St. Louis, Missouri that heightened tensions in the Border State. Tensions were high up to that day, as Missouri governor Claiborne F. Jackson, a secessionist that ran (possibly fraudulently) as a Stephen Douglas Democrat, called out the Missouri State Guard for drill at a location near the present campus of St. Louis University in early May. That April, a pro-Confederate mob had seized arms from the federal arsenal at Liberty, Missouri, near Kansas City. This action aroused fears that the arsenal in St. Louis, the largest in any of the slave states, was a target.
In response, Capt. Nathaniel Lyon, who was placed as acting commander of the Army’s Department of the West, began enlisting and equipping Union militia in preparation for an attack against the arsenal. Union forces quickly moved a significant number of the weapons in the arsenal to Illinois for safety, which caused Jackson to call out the militia. The site they drilled at was quickly dubbed Camp Jackson. The presence of the militia, as well as the recent acquisition of munitions and weapons from the Confederate government (which were seized from a federal arsenal at Baton Rouge), caused Lyon great concern and he marched a force of approximately six thousand against Camp Jackson on May 10.
The Missouri State Guard was greatly outnumbered and Lyon soon place the almost seven hundred militia members under arrest and proceeded to march them back into the city. In the meantime, the native-born citizens of St. Louis, largely hostile to the Germans in Lyon’s force began to assemble and heckle the Union forces as they marched back through the city. The Union forces faced rocks and other objects, as well as insults being thrown at them. Speculation abounds as to who fired a shot, but a shot was fired, fatally wounding Capt. Constantin Blandowski, who was Polish, but considered German. His regiment fired over, then into the crowd, which began a period of shooting and rioting that left almost thirty dead and dozens wounded.
The aftermath of the incident caused native-born citizens to attack Germans in retaliation for humiliating the militia and over fears of Germans killing locals. If forced citizens to choose sides in the war, but is believed to have kept Missouri in the Union. The incident is important for illustrating the fierce divisions in America during the war and for the importance of German-Americans to the Union cause. Nathaniel Lyon was quickly promoted to Brigadier General and would be killed later that year commanding Union troops at the Battle of Wilson’s Creek. Today, the site is commemorated by a marker that I hope to visit when I head home to Illinois in June.
Civil War History 
My opinion is that if Lyon had not taken the prisoners, the War in Missouri would probably not occurred, at least to the extent that it did. The political conditions before Camp Jackson would have never approved the formation of the Missouri State Guard, Gov. Jackson would never have been granted dictatorial powers by the State legislature, and its Commander, Gen. Sterling Price would have remained a moderate Union man. (Instead, he became a Confederate General) Gov. Jackson’s illegal munitions would have remained in a store house and possibly retrieved by the Union.