James L. Roark, et al., eds., The American Promise: A History of the United States, 2nd ed., vol. 1 (Boston: Bedford/St. Martin’s, 2002), 473.
Fighting broke out on the morning of May 21, 1856, when a mob of several hundred proslavery men entered the town of Lawrence, the center of free-state settlement. Only one man died - a proslavery raider who was killed when a burning wall collapsed - but the 'Sack of Lawrence,' as free-soil forces called it, inflamed northern opinion. In Kansas, news of Lawrence provoked one free-soil settler, John Brown, to 'fight fire with fire.' Announcing that 'it was better that a score of bad men should die than that one man who came here to make Kansas a Free State should be driven out,' he led the posse that massacred five allegedly proslavery settlers along the Pottawatomie Creek. After that, guerilla war engulfed the territory.