“Further information: see Bleeding Kansas and Missouri in the American Civil War
The Missouri-Kansas border area was fertile ground for the outbreak of guerrilla warfare when the Civil War erupted in 1861. Historian Albert Castel wrote:
For over six years, ever since Kansas was opened up as a territory by Stephen A. Douglas’ Kansas-Nebraska Bill of 1854, its prairies had been the stage for an almost incessant series of political conventions, raids, massacres, pitched battles, and atrocities, all part of a fierce conflict between the Free State and proslavery forces that had come to Kansas to settle and to battle.[1]
In February 1861 Missouri voters elected delegates to a statewide convention, which rejected secession by a vote of 89-1. Unionists, led by regular US army commander Nathaniel Lyon and Frank Blair of the politically powerful Blair family, and increasingly pro-secessionist forces, led by governor Claiborne Jackson and future Confederate general Sterling Price, contested for the political and military control of the state. By June, there was open warfare between Union forces and troops supporting the Confederacy. Guerrilla warfare immediately erupted throughout the state and intensified in August after the Union defeat at the Battle of Wilson’s Creek.[2]
By August 1862, with the Union victory at the Battle of Pea Ridge, the state was free of significant regular Confederate troops but the violence in Missouri continued. One historical work describes the situation in the state after Wilson’s Creek:
Unlike other border areas in Maryland and Kentucky, local conflicts, bushwacking, sniping, and guerilla fighting marked this period of Missouri history. “When regular troops were absent, the improvised war often assumed a deadly guerrilla nature as local citizens took up arms spontaneously against their neighbors. This was a war of stealth and raid without a front, without formal organization, and with almost no division between the civilian and the warrior.”[3]
The most notorious of these guerrilla forces was led by William Clarke Quantrill.”
http://en.wikipedia.org/wiki/Quantrill%27s_Raiders