American Civil War: The Confederate States of America accept a rival state government's pronouncement that declares Missouri to be the 12th state of the Confederacy.

The American Civil War was a civil war in the United States between the Union and the Confederacy, which was formed in 1861 by states that had seceded from the Union. The central conflict leading to war was a dispute over whether slavery should be permitted to expand into the western territories, leading to more slave states, or be prohibited from doing so, which many believed would place slavery on a course of ultimate extinction.

The Confederate States of America (CSA), also known as the Confederate States (C.S.), the Confederacy, or the South, was an unrecognized breakaway republic in the Southern United States from 1861 to 1865. It comprised eleven U.S. states that declared secession: South Carolina, Mississippi, Florida, Alabama, Georgia, Louisiana, Texas, Virginia, Arkansas, Tennessee, and North Carolina. These states fought against the United States during the American Civil War.

During the lead-up to the American Civil War, the proposed secession of Missouri from the Union was controversial because of the state's disputed status. The Missouri state convention voted in March 1861, by 98-1, against secession, and was a border state until abolishing slavery in January 1865. Missouri was claimed by both the Union and the Confederacy, had two rival state governments,, and sent representatives to both the United States Congress and the Confederate Congress.

During the American Civil War, Missouri was a hotly contested southern border state populated by both Union and Confederate sympathizers. It sent armies, generals, and supplies to both sides, maintained dual governments, and endured a bloody neighbor-against-neighbor intrastate war within the larger national war.