When the Civil War began, Cass County, Missouri, held more than 1,700 families, including 8,900 free whites and 1,000 slaves, many of them migrants from Kentucky, Tennessee, and Virginia whose southern culture shaped a growing and prosperous county, but the conflict forced neighbors and even families onto opposite sides as violence along the Missouri-Kansas border became personal and fell heavily on civilians. The wider border struggle had deepened after Missouri entered the Union as a slave state in 1821 and Congress passed the Kansas-Nebraska Act in 1854, opening Kansas Territory to a vote on slavery, which drew in abolitionists and free-staters as well as pro-slavery Missourians, led to disputed elections in 1855, and brought six years of murder, looting, and revenge known as Bleeding Kansas. During the Civil War, some of the same Kansas men who had fought in that earlier conflict served in Union commands, and western Missouri was ravaged in the winter of 1861-62 by forces including the 7th Kansas Cavalry, Jennison's Jayhawkers, Jim Lane's Brigade, and redleg units, while Missouri guerrilla bands, or bushwackers, formed in response, with William Quantrill becoming the best-known leader. At sunrise on August 21, 1863, Quantrill led about 400 men into Lawrence, Kansas, burned more than 180 buildings, and killed more than 150 men and boys before retreating into Cass County. Four days later Brigadier General Thomas Ewing, commanding the District of the Border, issued General Orders No. 11, covering Jackson, Cass, Bates, and northern Vernon counties and requiring the evacuation within 15 days of civilians from the district except in Kansas City, Independence, Hickman Mills, Pleasant Hill, and Harrisonville. Intended to deny bushwackers and southern sympathizers food, water, and shelter and to discourage retaliation, the order drove some 20,000 people from their homes, many of them women, children, and elderly people who left behind barns, fields, orchards, harvests, and household goods and often walked in dust and heat with only what they could carry. Immediately after the Lawrence raid, Charles "Doc" Jennison was authorized to raise the 15th Kansas Cavalry, and that regiment with other Union units entered Missouri to enforce Ewing's order. During August, September, and October 1863, Union troops and forage teams systematically confiscated grain and hay, harvested standing crops, collected livestock, and burned homes, barns, and other structures that might shelter bushwackers; some Union families' homes were spared only to be burned later by southern bushwackers. Across western Missouri, many homesteads were reduced to charred chimneys called Jennison's Tombstones, and the devastated region became known as the Burnt District.