How did John Brown's raid at Harpers Ferry affect the outcome of the Civil War?

On October 16, 1859, abolitionist John Brown and his 22 followers staged an armed attack on the town of Harpers Ferry, West Virginia. Brown's intention was to seize control of the US armory in Harpers Ferry and use the guns contained there to arm the slaves, setting off a rebellion that would end slavery in the United States.
Brown and his family had a long history of involvement in radical abolitionism. For the several years before the raid, Brown and his sons were prominent figures in the violent guerrilla conflict between abolitionist and pro-slavery forces in Kansas. After pro-slavery guerrillas raided the abolitionist stronghold of Lawrence in 1856, Brown and his sons killed five pro-slavery men living along Pottawatomie Creek in a retaliatory raid. In 1857, Brown left Kansas for the east coast to raise money and recruit men for his planned attack on Harpers Ferry.
Brown's raid on Harpers Ferry was a tactical failure, as his tiny uprising was crushed by U.S. forces led by Robert E. Lee and J.E.B. Stuart—two men who became Confederate generals when the Civil War started less than two years later. Brown was hung for treason, although not before making a final statement that "the crimes of this guilty land will never be purged away but with blood."
However, Brown's tactical failure was a strategic victory. With his violent attack on Harpers Ferry, the mood of the nation became completely polarized. People were no longer willing to search for yet another compromise on the question of slavery and became determined to fight it out and resolve the issue once and for all. After Abraham Lincoln was elected president in 1860, a total of 11 states eventually seceded and declared their independence as the Confederate States of America.
In the Civil War that followed, 620,000 soldiers on both sides were killed before the Confederacy eventually surrendered in 1865. Slavery was abolished in the United States just six years after Brown's attack on Harpers Ferry. Although the raid happened before what most people think of as the official beginning of the Civil War, it arguably made the Civil War inevitable.
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