The Kansas-Nebraska Act was introduced in 1854 by Illinois Democrat Stephen Douglas to create the territories of Kansas and Nebraska. Within, it also introduced the idea of “popular sovereignty,” in which residents of Kansas Territory would vote on whether or not to enter the Union as free-states or slave-states. Its enactment effectively repealed the Missouri Compromise of 1820, which outlawed slavery north of the 36º30' parallel north (Missouri’s southern border). In a United States already locked in debate over enslavement, the Kansas-Nebraska Act of 1854 further aggravated tensions.