The Nebraska-Kansas Act proposed by Stephen Douglas allowed settlers in Kansas and Nebraska territories to decide through popular sovereignty whether to allow slavery, repealing the Missouri Compromise. This led pro-slavery and anti-slavery settlers to rush to the territories to influence the vote, sparking violence between the groups known as Bleeding Kansas. After several years, Kansas was admitted to the union as a free state in 1861, deepening the national divide over slavery and contributing to the onset of the Civil War.