Bleeding Kansas:

Bleeding Kansas was a mini Civil War that was going on in the Kansas territory. After the Kansas-Nebraska Act of 1854, which allowed slavery in the Kansas territory (which was originally banned by the Missouri Compromise), many abolitionists began to revolt against slaveholders, freed some slaves, and lost many of their own in the fight. The leader, John Brown, even lost one of his sons due to the fighting.
http://www.pbs.org/wgbh/aia/part4/4p2952.html

Source: Horton, James Oliver, and Lois E. Horton. Slavery and the Making of America. New York: Oxford, 2006. 156-157.