Camp Jackson affair

38°38′12″N 90°14′12″W / 38.636551°N 90.236721°W / 38.636551; -90.236721

The Camp Jackson affair, also known as the Camp Jackson massacre, occurred during the American Civil War on May 10, 1861, when a volunteer Union Army regiment captured a unit of secessionists at Camp Jackson, outside the city of St. Louis, in the divided slave state of Missouri.

The newly appointed Union commander in Missouri, Brigadier General Nathaniel Lyon, had learned that the ostensibly-neutral state militia training in Camp Jackson was planning to raid the federal arsenal in St. Louis. That led to him and his regiments, consisting mostly of pro-Union German immigrants, marching into St. Louis and capturing the rebels. After capturing the entire unit, Lyon marched the captives into town to parole them. En route, hostile secessionist crowds gathered and began throwing rocks and shouting ethnic slurs at Lyon's regiments, and after an accidental gunshot, Lyon's men fired into the mob, killed at least 28 civilians, and injured dozens of others. Several days of rioting throughout St. Louis followed. The violence ended only after martial law had been imposed and Union regulars dispatched to the city.

Lyon's actions ensured Union control of St. Louis and Missouri for the rest of the war but also deepened the ideological divisions within a state that had initially sought to remain neutral in the larger conflict.