Answer: It led to unrest and violence between pro-slavery and anti-slavery groups.
Context/details:
The Kansas-Nebraska Act enacted by Congress in 1854. It granted popular sovereignty to the people in the Kansas and Nebraska territories, letting them decide whether they'd allow slavery. In essence, this made the Kansas-Nebraska act a repeal of the Missouri Compromise of 1820, which had said there would be no slavery north of latitude 36°30´ except for Missouri.
After the passage of the Kansas-Nebraska Act, pro-slavery and anti-slavery settlers rushed into Kansas to try to sway the outcome of the issue, and violence between the two sides occurred. The term "bleeding Kansas" was used because of the bloodshed.