Sectional tensions over slavery began to increase in the early part of the 19th century when the United States began acquiring new territory. Abolitionists wanted the new territories to be free, while slave-holding interests wanted slavery in the new lands.
The passing of the Missouri Compromise in 1820 was a critical juncture in the debate between the free North and slave-holding South over slavery in the United States. According the Library of Congress, Maine was admitted to the Union as a free state, while Missouri was admitted as a slave state. The Missouri Compromise was repealed in 1850 by the Kansas-Nebraska act, which left the issue of slavery to the residents of the new states. This resulted in much tension and bloodshed as pro- and anti-slavery settlers raced to settle Kansas.