William Quantrill joined the Confederate Army on the outbreak of the American Civil War. He fought at Lexington but disliked the regimentation of army life and decided to form a band of guerilla fighters. As well as attacking Union troops the Quantrill Raiders also robbed mail coaches, murdered supporters of Abraham Lincoln and persecuted communities in Missouri and Kansas that Quantrill considered to be anti-Confederate. He also gained a reputation for murdering members of the Union Army that the gang had taken prisoner.

In 1862 Quantrill and his men were formally declared to be outlaws. By 1863 Quantrill was the leader of over 450 men. This included Frank James, Jessie James, Cole Younger and James Younger. With this large force he committed one of the worst atrocities of the Civil War when he attacked the town of Lawrence. During the raid on 21st August, 1863, Quantrill's gang killed 150 inhabitants and destroyed over 180 buildings.

The district Union commander, General Thomas Ewing, was furious when he heard what the Quantill Raiders had done. On 25th August 1863, he issued Order No 11. This gave an eviction notice to all people in the area who could not prove their loyalty to the Union cause. Ewing's decree virtually wiped out the entire region. The population of Cass County dropped from 10,000 to 600.

Quantrill found it difficult to keep his men under control and they tended to go off and commit their own crimes. By 1865 he had only 33 followers left. On 10th May 1863 Quantrill was ambushed by federal troops. William Quantrill was shot and died from his wounds on 6th June, 1865.