In 1854, the Kansas-Nebraska Act created two territories: Kansas and Nebraska. It also replaced the Missouri Compromise of 1820, which had prohibited slavery in new territories north of the 36°30′ line of latitude. Instead, according to the act, white male settlers would determine whether they would permit slavery in their territory through popular sovereignty. As a result, anti-slavery settlers (“Freesoilers”) and pro-slavery settlers (“Border Ruffians”) began moving to Kansas in high numbers. They intended to influence the vote of whether slavery was in or out. The violent armed conflicts that followed between these two groups became known as “Bleeding Kansas.” This set of resources provides background information, including primary sources, on this conflict. Students should consider these resources when analyzing the positives and negatives of using popular sovereignty to permit or ban slavery in new territories.