President James Monroe issued the proclamation that completed Missouri’s admission to the Union as the twenty-fourth state. The event carried significance far beyond the creation of another state government. Missouri’s admission concluded a prolonged congressional struggle over slavery’s expansion into western territories and established a political settlement that shaped national policy for more than three decades. The dispute exposed the growing sectional division between free and slave states and demonstrated that territorial expansion had become inseparable from the question of slavery in the United States.
Missouri had formed from land acquired by the United States through the Louisiana Purchase of 1803. American migration into the region accelerated during the early nineteenth century, particularly after the War of 1812. By 1818, Missouri Territory had developed sufficient population and political organization to seek admission as a state. Its application immediately created a national controversy because slavery already existed within the territory. At the time, the Senate contained an equal number of free and slave states, making Missouri’s proposed admission important to the sectional balance of political power.
The controversy intensified in February 1819 when Representative James Tallmadge Jr. of New York proposed amendments to Missouri’s enabling legislation. His proposal would have prohibited the further introduction of enslaved people into Missouri and provided for the eventual emancipation of children born to enslaved parents there. The House approved restrictions, but the Senate rejected them. The dispute raised fundamental constitutional and political questions concerning congressional authority over slavery in territories and prospective states. Southern legislators resisted congressional restrictions on Missouri, while many northern legislators opposed the unrestricted extension of slavery into lands acquired by the federal government.
Congress eventually resolved the immediate conflict through legislation known collectively as the Missouri Compromise. Passed in March 1820, the settlement permitted Maine, formerly part of Massachusetts, to enter the Union as a free state and authorized Missouri to organize for admission without requiring the abolition of slavery. Maine became the twenty-third state on March 15, 1820. The legislation also prohibited slavery in the remaining Louisiana Purchase territory north of latitude 36 degrees 30 minutes, except within Missouri. This arrangement preserved the numerical balance between free and slave states in the Senate while establishing a geographic restriction on slavery within much of the Louisiana Purchase.
Missouri drafted a state constitution during the summer of 1820, but admission encountered another obstacle. A provision in the constitution directed the state legislature to enact laws preventing free Black people and mulattoes from entering Missouri. Members of Congress objected that such a provision could conflict with the federal Constitution’s Privileges and Immunities Clause by restricting the rights of citizens from other states. The resulting dispute produced what historians often identify as the second Missouri crisis. Congress approved another compromise on March 2, 1821, requiring Missouri to provide assurances that its constitution would never be interpreted to authorize legislation excluding citizens of other states from rights guaranteed by the federal Constitution.
Missouri’s legislature adopted the required resolution, allowing Monroe to complete the admission process. On August 10, 1821, the president issued Proclamation 28. Monroe declared that Missouri’s admission into the Union was complete after determining that the state had satisfied the congressional condition. Secretary of State John Quincy Adams formally attested the proclamation. With that act, Missouri became the twenty-fourth state and the first state formed entirely from the Louisiana Purchase, apart from Louisiana itself, to enter the Union west of the Mississippi River.
The political importance of Missouri statehood endured long after August 1821. The Missouri Compromise established a federal framework for managing the expansion of slavery as the nation moved westward, but it did not settle the underlying sectional conflict. Instead, it demonstrated how strongly control of the Senate, western settlement, federal authority, and slavery had become connected. The compromise line remained central to national politics until the Kansas-Nebraska Act of 1854 effectively repealed the restriction by permitting settlers in western territories to determine the slavery question through popular sovereignty. Three years later, the Supreme Court’s decision in Dred Scott v. Sandford declared the congressional restriction on slavery in the territories unconstitutional.
Missouri’s admission therefore marked both the successful expansion of the federal Union and a major stage in the developing sectional crisis. August 10, 1821, formally established Missouri as a state, but the legislative struggle preceding statehood revealed divisions that continued to deepen during the following four decades. The Missouri controversy established slavery’s western expansion as a central national political issue and foreshadowed the repeated sectional crises that ultimately culminated in the Civil War.
References / More Knowledge:
Library of Congress. “Missouri Compromise: Primary Documents in American History.” Library of Congress. https://guides.loc.gov/missouri-compromise
Library of Congress. “Today in History—August 10: The ‘Show Me’ State.” Library of Congress. https://www.loc.gov/item/today-in-history/august-10/
National Archives and Records Administration. “Missouri Compromise (1820).” Milestone Documents. https://www.archives.gov/milestone-documents/missouri-compromise
National Archives and Records Administration. “Presidential Proclamation 28 of August 10, 1821, by President James Monroe Declaring the Admission of the State of Missouri as a Member of the Union to Be Complete.” DocsTeach. https://docsteach.org/document/presidential-proclamation-28-of-august-10-1821-by-president-james-monroe-declaring-the-admission-of-the-state-of-missouri-as-a-member-of-the-union-to-be-complete/
Missouri Secretary of State. “Timeline of Historic Missouri: 1821–1860.” Missouri State Archives. https://www.sos.mo.gov/archives/history/timeline/2
Missouri Secretary of State. “Before Dred Scott: Antebellum Missouri.” Missouri State Archives. https://www.sos.mo.gov/archives/education/aahi/beforedredscott/antebellum_mo
United States Senate Historical Office. “Missouri Compromise Ushers in New Era for the Senate.” United States Senate. https://www.senate.gov/artandhistory/history/minute/Missouri_Compromise.htm
United States Senate Historical Office. “Constitution Day 2018: On Equal Footing—The Missouri Crisis of 1820.” United States Senate. https://www.senate.gov/about/origins-foundations/senate-and-constitution/constitution-day-2018-missouri-crisis.htm
The American Presidency Project. “Proclamation 28—Admitting Missouri to the Union.” University of California, Santa Barbara. https://www.presidency.ucsb.edu/documents/proclamation-28-admitting-missouri-the-union