The Kansas-Nebraska Act may have been the single most significant event leading up to the Civil War. By the early 1850s, settlers and entrepreneurs wanted to move into the area now known as Nebraska. However, until the area was organized as a territory, settlers would not move there because they could not legally hold a claim on the land. The southern states' representatives in Congress were in no hurry to permit a Nebraska territory because the land lay north of the 36°30' parallel — where slavery had been outlawed by the Missouri Compromise of 1820.
The person behind the Kansas-Nebraska Act was Senator Stephen A. Douglas of Illinois. Douglas supported building a transcontinental railroad that would go through Chicago, Illinois. Since the railroad would also go through Nebraska, Nebraska would need to become a new territory. To win southern support, he proposed simultaneously creating a state many thought would be inclined to support slavery: Kansas.
The Kansas-Nebraska Act allowed each territory to decide the issue of slavery itself, a concept called "popular sovereignty."

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