The British ceded the area that is now Mississippi to the U.S. in 1783 under the Treaty of Paris, which ended the Revolutionary War. In 1802 the State of Georgia withdrew its claims on land in Mississippi, which went back to the colonial era. Mississippi was under federal territorial governance following the Northwest Ordinance model.
The Louisiana Purchase diminished the influence of longstanding French and Spanish interests in lands west of Georgia. American settlers and U.S. interests created pressure on lands west of Florida and made Spanish withdrawal inevitable. As the Spanish regime in Florida receded, the area that later would become Alabama and Mississippi extended south to the coast of the Gulf of Mexico.
Mississippi followed what had become the pattern of development for southern territories that became southern states. Indian tribes were pushed west and slaves were brought in by white settlers to provide the labor for an agrarian economy. The invention of the cotton gin jump-started the plantation system that would produce incredible wealth and result in demographic patterns that included numbers of slaves that were far greater than those of the white settlers.
In 1810 the territorial Delegate in the U.S. House of Representatives introduced a statehood enabling act, and Mississippi’s territorial legislature endorsed statehood as well. It was the start of political jousting over the huge size of the territory and the idea that it should be divided… and the impact of having two Southern slave states compared with one very large one. Discussion on the impact of the two options on the balance between Southern and Northern states continued until the outbreak of the War of 1812. Serious attention to the admission of a new state did not resume until 1815.
During the hiatus of 1813 through 1815 an all-consuming local land claim scandal that might have derailed statehood was resolved under federal territorial law, making the right time to address statehood. However, a bill introduced by the Mississippi territory’s Delegate to authorize a local constitutional convention and petitions of the territorial legislature largely were ignored by Congress.
So it was in 1816 after the land claims scandal was no longer a prominent problem and increased migration was driving economic growth that the issue of statehood became ripe. But by then the issue of division of the territory into two states had grown more complicated for the very reason that most migration settled in the eastern half of the Mississippi territory. Making the whole territory a single state would give the newcomers in the east political domination over western Mississippi.
The territorial Delegate favored dividing the territory into two states, but the easterners petitioned for admission of the territory as one state. The admission of Indiana in that year had given the north one more state than the south, and Congress decided the most expedient way to restore North-South parity was to divide Mississippi, admit the western half as a state, and organize the eastern half until it was ready for admission at a later time.
Accordingly, in March of 1817 an enabling act for admission of western Mississippi as a state took effect, by December a state constitution was in place, and on December 10, 1817, before another year ended, Mississippi became the 20th State of the Union. The 1817 enabling act for Mississippi also was an organic act establishing the territory of Alabama as the first step toward its admission as a state.