Bleeding Kansas was brought about because?

Answer 1

The 'Popular Sovereignty' vote - a hopeful plan to let the local population decide whether the new state was to be slave or free.

It was looking like a close-run contest, so many fanatics from both sides of the debate crossed into Kansas to buy cheap properties that would give them the vote.

Many of these people intimidated the locals and tried to get the ballot declared void. Some of them (including John Brown) inflicted violence too, which rapidly escalated.

Answer 2

Bleeding Kansas, Bloody Kansas or the Border War, was a series of violent events, involving anti-slavery Free-Staters and pro-slavery "Border Ruffian" elements, that took place in the Kansas Territory and the western frontier towns of the U.S. state of Missouri roughly between 1854 and 1858. At the heart of the conflict was the question of whether Kansas would enter the Union as a free state or slave state. As such, Bleeding Kansas was a proxy war between Northerners and Southerners over the issue of slavery in the United States. The term "Bleeding Kansas" was coined by Horace Greeley of the New York Tribune; the events it encompasses directly presaged the American Civil War.