1819 – The United States House of Representatives passes the Missouri Compromise for the first time. The Missouri Compromise (also known as the Compromise of 1820) was federal legislation of the United States that balanced the desires of northern states to prevent the expansion of slavery in the country with those of southern states to expand it. It admitted Missouri as a slave state and Maine as a free state and declared a policy of prohibiting slavery in the remaining Louisiana Purchase lands north of the 36°30′ parallel. The 16th United States Congress passed the legislation on March 3, 1820, and President James Monroe signed it on March 6, 1820. Earlier, in February 1819, Representative James Tallmadge Jr., a Democratic-Republican (Jeffersonian Republican) from New York, had submitted two amendments to Missouri's request for statehood that included restrictions on slavery. While the slave states earlier claimed Federal protection for slavery, they now objected to any bill that imposed federal restrictions on slavery and claimed that it was a state issue, as settled by the Constitution. However, with the Senate evenly split at the opening of the debates, both sections possessing 11 states, the admission of Missouri as a slave state would give the South an advantage. Northern critics including Federalists and Democratic-Republicans objected to the expansion of slavery into the Louisiana Purchase territory on the Constitutional inequalities of the three-fifths rule, which conferred Southern representation in the federal government derived from a state's slave population. Jeffersonian Republicans in the North ardently maintained that a strict interpretation of the Constitution required that Congress act to limit the spread of slavery on egalitarian grounds. "[Northern] Republicans rooted their antislavery arguments, not on expediency, but in egalitarian morality." "The Constitution [said northern Jeffersonians], strictly interpreted, gave the sons of the founding generation the legal tools to hasten [the] removal [of slavery], including the refusal to admit additional slave states." When free-soil Maine offered its petition for statehood, the Senate quickly linked the Maine and Missouri bills, making Maine's admission a condition for Missouri entering the Union as a slave state. The Missouri Compromise was controversial. While it mollified most people at the time and settled the issue for more than 20 years, many worried that the country had become lawfully divided along regional and sectarian lines. Tensions resumed in the 1840s and the Compromise of 1850 only briefly defused the situation. The Kansas–Nebraska Act effectively repealed the bill in 1854, and the Supreme Court declared it unconstitutional in Dred Scott v. Sandford (1857), both of which increased tensions over slavery and contributed to the American Civil War. The compromise both delayed the Civil War and sowed its seeds; in April 1820, Thomas Jefferson predicted the line as drawn would someday tear the Union apart. Forty years later, the North and South would split closely along the 36°30′ parallel and launch the Civil War.
