After years of small-scale civil war, Kansas was admitted into the Union as a free state under the "Wyandotte Constitution" on January 29, 1861. Most people gave strong support to the Union cause. However, guerrilla warfare and raids from pro-slavery forces, many spilling over from Missouri, occurred during the Civil War. Although only one battle of official forces occurred in Kansas, there were 29 Confederate raids into the state during the war and numerous deaths caused by the guerrillas. Lawrence came under attack on August 21, 1863, by guerrillas led by William Clarke Quantrill. He was retaliating for "Jayhawker" raids against pro-Confederate settlements in Missouri. His forces left more than 150 people dead in Lawrence.