In 1854 the Kansas-Nebraska act overturning the Missouri compromise's use of latitude as the boundary between slave and free territory and instead using the principal of popular sovereignty. Free state and pro slave settlers rushed into Kansas to try to influence the decision. Soon enough violence erupted as they fought for who would take control. John Brown an abolitionist who led the anti-slave fighters in Kansas before his famed raid Harper's Ferry
Violence erupts because Anti-slave people and Pro slave people were at the point where they basically have to fight and kill just for Kansas to become a free or slave state.
“Bleeding Kansas” was first fixed on that strife-ridden territory by antislavery publicists. The opening of the Kansas and Nebraska territories in 1854 under the principle of popular sovereignty provoked a protracted political crisis in both Kansas and the nation at large. Rival governments had been established in Kansas by late 1855, one backed by pro slavery Missourians, the other by antislavery groups.
Civil conflict in Kansas accompanied the political polarization. The volatility to be expected of a frontier area was compounded by the activities of parties interested in the slavery issue both the Missourians and the northerners who reputedly shipped free-state settlers and armaments to the region.
Hostilities between armed bands seemed imminent in late 1855 as well over a thousand Missourians crossed the border and menaced Lawrence, a free-state stronghold. On May 21, 1856, ruffians actually looted that town. In response, John Brown orchestrated the murder several days later of five proslavery settlers along Pottawatomie Creek.
John W. Geary, appointed territorial governor in September, managed to cool the “border war” with the aid of federal troops. But Kansas had hardly ceased bleeding–as became apparent in 1858 with the Marais des Cygnes massacre of five free-state men and pronounced disorder in several counties. Although Kansans in that year once and for all rejected the proslavery Lecompton constitution, such violence continued on a smaller scale into 1861.