How did settlers in Kansas and nebraska were allowed to decide the slavery issue?

Settlers in Kansas and Nebraska were allowed to decide the slavery issue through the principle of "popular sovereignty," established by the Kansas-Nebraska Act of 1854. This act allowed the residents of these territories to vote on whether to permit slavery or not, effectively circumventing the Missouri Compromise. This led to significant conflict, known as "Bleeding Kansas," as pro-slavery and anti-slavery settlers rushed to the territories to influence the vote. The resulting violence highlighted the deep divisions over slavery in the United States.