On May 21, 1856, a large group of pro-slavery men rode in and sacked Lawrence, the Free-Soil capital of the Kansas Territory. The pro-slavery men especially had it in for the Lawrence Telegraph, the Free-Soil newspaper: they set fire to the building and destroyed the printing press. Brown, as it turned out, was not far away.

On learning that Lawrence was under attack, Brown mustered his militia company and marched. He did not reach Lawrence in time, and his men were demoralized to learn that the town had been sacked. Brown had some trouble holding them together until they learned that an attack of another kind had been made, and this one was committed in broad daylight, in the United States Senate.