The U.S. federal government was supported by 20 mostly-Northern free states in which slavery already had been abolished, and by five slave states that became known as the border states. All of the Midwestern states but one, Missouri, banned slavery. Though most battles were fought in the South, skirmishes between Kansas and Missouri continued until culmination with the Lawrence Massacre on August 21, 1863. Also known as Quantrill's Raid, the massacre was a rebel guerrilla attack by Quantrill's Raiders, led by William Clarke Quantrill, on pro-Union Lawrence, Kansas. Quantrill's band of 448 Missouri guerrillas raided and plundered Lawrence, killing more than 150 and burning all the business buildings and most of the dwellings. Pursued by federal troops, the band escaped to Missouri.