The Missouri State Guard (MSG) was a military force established by the Missouri General Assembly on May 11, 1861. While not a formation of the Confederate States Army, the Missouri State Guard fought alongside Confederate troops and, at various times, served under Confederate officers.

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.