The Kansas-Nebraska Crisis developed in relation to a number of other key events that were occurring in the United States during the first half of the 19th Century. Following independence and with the growth of manufacturing, a growing divide occurred in the United States surrounding the issue of slavery. In the North, states banned slavery and saw it as a backwards and "peculiar" institution. In the South, slavery was a key aspect of the economy, as it was slave labor that built the wealth of the South through crops like cotton. As this issue grew more divisive, both sides feared the opposing side gaining a majority in Congress, as this could lead to the passing of federal laws either to preserve slavery or to ban it across the United States. One way to keep this divisive issue from tearing the country apart entirely was to maintain a balance between the number of free states and the number of slave states in the U.S. This would mean that there would be an equal number of free and slave state senators, and no federal laws about slavery could easily be passed.
With the purchase of the Louisiana territory from France in 1803, the United States gained an enormous piece of land and settlers began to head west from the coast to settle this land. Internal improvements, such as roads, canals, and eventually the railroad, would help to speed this process up. As more people moved into the territories making up the Louisiana Purchase, there were efforts to organize the territory into states. Between the years of 1816 to 1819, for example, four new states were added to the country. Two of these states (Indiana and Illinois) were free states, while two were slave states (Mississippi and Alabama). There was an effort to maintain this balance in order to preserve the country despite disagreement over the institution of slavery.
In 1820, Missouri would apply to enter the United States as a slave state; however, this would upset the balance between free and slave states. Eventually a compromise was reached that would allow Missouri to enter the Union as a slave state, while Maine would be created as a free state. They also established the 36-30 latitude line as a division regarding the admission of future states. Any future new states north of the line would be free, and any future new states south of the line would be slave.
Following the Mexican-American War, the United States gained more land to its west. The following gold rush in California would quickly establish California as a state. Under the Compromise of 1850, California would be admitted as a free state, but to appease Southerners, a new and stricter fugitive slave act would be created as well. There also came a growing desire to build a transcontinental railroad across the country to link California and the west coast with the rest of the United States. As a result, pressure rose to organize the territories of Kansas and Nebraska so that the railroad would be built through them. This, however, would upset the balance between free and slave states, as both Kansas and Nebraska were above the 36-30 line. In attempt to solve this problem, Illinois politician Stephen A. Douglas proposed the idea that the status of slavery in Kansas and Nebraska would be decided by popular sovereignty—or by allowing the settlers there to vote on the issue.
The Kansas-Nebraska Act, which followed Douglas's proposal, was passed. It also repealed the 36-30 line established by the Missouri Compromise. The result, however, did not bring a peaceful solution. The Kansas-Nebraska Act was hated by northerners and celebrated across the South. It also led to the settlement of these territories, particularly Kansas, by both pro-slavery and anti-slavery settlers, each trying to help determine the status of slavery in these territories. The result was violence and death between the two groups as they came into close contact. This would lead to the use of the term "Bleeding Kansas" to describe the crisis that would occur there. Some historians also cite this outbreak of violence as the true start of the Civil War conflict.
While the Kansas-Nebraska Act attempted to help settle and organize land in the west, and bring about a solution to the question of whether or not Kansas and Nebraska would be free or slave, it instead brought about conflict. This deepened already heated divisions between the North and South regarding the issue of slavery. It is for this reason that the Kansas-Nebraska Crisis is often mentioned when examining the causes of the American Civil War.