John Brown:
John Brown was a leading figure in the abolitionist movement in the pre-Civil War United States. Unlike many anti-slavery activists, he was not a pacifist and believed in aggressive action against slaveholders and any government officials who enabled them.
John Brown's plan seemed fairly straightforward: he and his men would establish a base in the Blue Ridge Mountains from which they would assist runaway slaves and launch attacks on slaveholders. At least that was the plan that the militant abolitionist had described to potential funders in 1857.
Well in the third answer:
Bleeding Kansas describes the period of repeated outbreaks of violent guerrilla warfare between pro-slavery and anti-slavery forces following the creation of the new territory of Kansas in 1854. In all, some 55 people were killed between 1855 and 1859.