Bleeding Kansas is used to describe the period of violence during the settling of territories in Kansas and Nebraska. In 1854, the Kansas-Nebraska Act was passed in response to complaints that settlers could not lay claim to homesteads because both areas had not yet been organized into territories. However, Southern congressmen were not especially enthusiastic about admitting Nebraska and Kansas into the Union as the areas lay north of the 36 30' parallel (this is the area populated by free states). The Missouri Compromise of 1820 had effectively established this imaginary line to separate free and slave states.
Now, with the Kansas-Nebraska Act, both Kansas and Nebraska would get to decide whether either would be a free or slave state. This effectively destroyed the fragile peace secured by the Missouri Compromise. With passage of the controversial Kansas-Nebraska Act, hostilities erupted in a bid to decide the fate of Kansas as either a slave or free state (Nebraska was further north and its fate as a free-state was never in question). Bloody conflict erupted between thousands of Northerners (who descended on Kansas to try to influence the make-up of the new state legislature) and Missourians, who poured over the border into Kansas to vote for a pro-slavery legislature.
The Northerners set up their Free-state legislature in Topeka, while the Missourians eventually moved their pro-slavery state legislature to Lecompton. There were now two opposing state legislatures in Kansas. The violence continued unabated. Pro-slavery factions tarred, feathered, and killed free-state militiamen. The abolitionist John Brown led an attack on pro-slavery men at Pottawatomie Creek. Five pro-slavery men were dragged from their homes and hacked to death. The Marais des Cynges massacre killed five free-state men. The terrible violence continued until a new governor, John W. Geary arrived to restore order in Sept. 1865. Bleeding Kansas became one of the most important triggers for the Civil War.