The Missouri Constitutional Convention of 1861–1863 was a constitutional convention held in the state of Missouri during the American Civil War. The convention was elected in early 1861, and voted against secession. When open fighting broke out between Pro-Confederate governor Claiborne Fox Jackson and Union authorities, and Union forces occupied the state capital, the convention formed a provisional state government, and functioned as a quasi-legislature for several years. The convention never did produce a new constitution; that task was delegated to a new convention, elected in 1864.
Missouri has had four constitutions:
The 1820 constitution provided for minor revisions to be made by amendment, but required that any general revision be carried out by an elected special convention. When secession was proposed, the Missouri General Assembly (the state legislature) voted that such a drastic change in the status of Missouri was comparable to such a general revision, that the General Assembly was not empowered to decide the issue, and called a convention.
The bill calling the convention passed on 17 January. The election was scheduled for 18 February, with three delegates chosen from each state senate district (99 total). In addition, by an amendment submitted by Charles H. Hardin, a secession declaration by the convention would have to be ratified in a referendum by a majority vote of the state's qualified voters. Hardin's amendment passed the state senate by only two votes, 17 to 15.
Three groups contended for the convention seats. One group called for Missouri to follow the Deep South slave states such as South Carolina by declaring secession immediately - not even waiting for Abraham Lincoln to take office as President.
Another group opposed secession at any time; they were the Unconditional Union Party.
A third group opposed immediate secession, but was willing to consider secession unless the various slavery-related political questions were resolved on terms acceptable to the slave states. These men were "conditional Unionists".