The Missouri Compromise of 1820 was an effort by the US Congress to resolve a sectional dispute between the 'free states' of the North and the 'slave states' of the South. Hoping to hinder the westward expansion of slavery – and thereby limit the undue political influence of the slave-holding South – Northern representatives had sought to deny Missouri admittance into the Union unless it limited slavery within its borders. This was hotly opposed by Southern representatives, leading to the compromise: Missouri would enter the Union as a 'slave state' in exchange for the admittance of Maine as a 'free state', as well as the prohibition of slavery in all western lands north of the 36°30′ parallel, excluding Missouri itself. While this provided a temporary solution, the question of slavery would only become more contested, eventually leading to the American Civil War (1861-1865).
This is a companion discussion topic for the original content at https://www.worldhistory.org/Missouri_Compromise/.