Why did violence break out in Kansas during Bleeding Kansas?

Violence erupted in the Kansas Territory during the period known as "Bleeding Kansas" (1854–1859) primarily due to the implementation of popular sovereignty under the Kansas-Nebraska Act.12

This doctrine allowed settlers in the territory to decide for themselves whether Kansas would enter the Union as a free or slave state. Rather than resolving the national debate over slavery, this policy triggered a desperate struggle for control. Proslavery advocates crossed the border from Missouri to influence the outcome, while antislavery forces from the North organized armed emigrant associations to populate the territory.312

The resulting political chaos led both factions to form guerrilla bands and regulating associations. Tensions escalated into open conflict, marked by events such as the Sack of Lawrence and the Pottawatomie Massacre, as each side sought to impose its vision for the future state through force. Ultimately, this period of bloodshed illustrated the failure of popular sovereignty to serve as a peaceful compromise between the nation's deeply divided factions.13