The KANSAS-NEBRASKA ACT OF 1854 may have been the single most significant event leading to the Civil War. By the early 1850s, settlers wanted to move into the area now known as Nebraska but refused to until it was made into a territory and they could lay claim to land there. Also, 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. He said he wanted to see Nebraska made into a territory and, to win southern support, proposed a southern state inclined to support slavery - Kansas. Underlying it all was his desire to build a transcontinental railroad to go through Chicago. The Kansas-Nebraska Act allowed each territory to decide the issue of slavery on the basis of popular sovereignty. The political effects of Douglas' bill were enormous and led to a rise in animosity between the North and the South.
The Railroad Background of the Kansas-Nebraska Act
The Mississippi Valley Historical Review, Vol. 12, No. 1 (Jun., 1925), pp. 3-22 (20 pages)
The Kansas-Nebraska Act: A Century of Historiography
The Mississippi Valley Historical Review, Vol. 43, No. 2 (Sep., 1956), pp. 187-212 (26 pages)
The Kansas-Nebraska Act and the Pacific Northwest Frontier
Pacific Historical Review, Vol. 22, No. 2 (1953), pp. 129-141 (13 pages)

The Kansas-Nebraska act made it possible for the Kansas and Nebraska territories (shown in orange) to open to slavery. The Missouri Compromise had prevented this from happening since 1820.
USHistory.org

Stephen Arnold Douglas (April 23, 1813 - June 3, 1861) was an American politician from Illinois. He served as a Representative, Senator, and the Democratic Party nominee for President in the 1860 election, losing to Republican Abraham Lincoln.
Stephen A. Douglas, American Politician. Photograph. Britannica ImageQuest, Encyclopædia Britannica, 19 Jan 2021.
quest.eb.com/search/139_3930065/1/139_3930065/cite. Accessed 18 Nov 2021.

KANSAS-NEBRASKA ACT, c1854. - Broadside, c1854, calling a mass meeting of anti-slavery settlers to address 'the important questions now before the people of Kansas' as a result of the Kansas-Nebraska Act.
Fine Art. Britannica ImageQuest, Encyclopædia Britannica, 25 May 2016.
quest.eb.com/search/140_1650520/1/140_1650520/cite. Accessed 18 Nov 2021.

KANSAS-NEBRASKA MAP, 1854. - Detail of a map of the United States showing the Kansas and Nebraska territories as they appeared following passage of the Kansas-Nebraska Act in 1854.
Fine Art. Britannica ImageQuest, Encyclopædia Britannica, 25 May 2016.
quest.eb.com/search/140_1647586/1/140_1647586/cite. Accessed 18 Nov 2021.