The Kansas-Nebraska Act was a bill that was passed into law in 1854 and established the territories of Kansas and Nebraska in the United States. It also had the effect of repealing the Missouri Compromise of 1820, which had banned slavery in much of the country. Spurred on by the efforts of Sen. Stephen Douglas of Illinois and Southern Democrats who wanted to extend slavery into parts of the United States still not settled, the law widened the rift between the North and the South and was one of the primary catalysts for the U.S. Civil War. Short-term effects of the Kansas-Nebraska Act included the formation of a new Republican party by those upset with the bill, and extensive violence in Kansas between pro-slavery and anti-slavery forces.
In the middle of the 19th century, the vast area west of Iowa and Missouri was one of the most attractive pieces of land still left unsettled in the United States. Settling the area was a necessity if the United States wanted to build a transcontinental railroad through the center of the country. Sen. Douglas, who chaired the Senate Committee on Territories, wanted the area settled so that his home state of Illinois could benefit from a potential railroad. He also saw a chance to enhance his presidential ambitions by pulling off such a major undertaking.
Pressured by Southern senators who declared that they would never allow the area to be settled without slavery being permitted, Douglas built upon the Compromise of 1850, which settled California and New Mexico while conceding to both sides of the slavery debate, by insisting that Kansas and Nebraska be governed by "popular sovereignty." This meant that each territory could make its own decision on the question of slavery. The implication of this would be that Nebraska would likely belong to the "free soilers" who opposed slavery and Kansas would become a slave territory.
Although reluctant at first to repeal the Missouri Compromise of 1820, which had banned slavery in all areas north of latitude 36° 30', President Franklin Pierce bowed to pressure from the Democratic Party and eventually supported the bill. The debate about the bill ended up being split more along territorial lines as opposed to party lines, with most Whigs and some moderate Democrats in the North teaming up to attempt to defeat the bill against the support of the heavily Democratic South. After months of debate, the Kansas-Nebraska Act gained enough support to be passed into law on May 30, 1854.
Passage of the Kansas-Nebraska Act so enraged some politicians in the North that they formed a new Republican Party, which would eventually replace the Whigs to become the second dominant party in the country. Kansas immediately became a battleground, as settlers on both sides of the slavery debate rushed in to form a territorial government. The violence that erupted caused the territory to be known as "bleeding" Kansas. On a larger scale, the furor raised by the act helped turn the long-standing rift between the North and South into an irrevocable impasse, setting the stage for the U.S. Civil War in 1861.