Abolitionist John brown hoped to spark a large-scale slave uprising that would sweep through the South.
On October 16, 1859, John Brown led a small army of 18 men into the small town of Harper's Ferry, Virginia. His plan was to instigate a major slave rebellion in the South. He would seize the arms and ammunition in the federal arsenal, arm slaves in the area and move south along the Appalachian Mountains, attracting slaves to his cause.
John Brown and his cohorts marched into an unsuspecting Harper's Ferry and seized the federal complex with little resistance. It consisted of an armory, arsenal, and engine house. He then sent a patrol out into the country to contact slaves, collected several hostages, including the great grandnephew of George Washington, and sat down to wait.
The slaves did not rise to his support, but local citizens and militia surrounded him, exchanging gunfire, killing two townspeople and eight of Brown's company.
Troops under the command of Lieutenant Colonel Robert E. Lee arrived from Washington to arrest Brown. They stormed the engine house, where Brown had withdrawn, captured him and members of his group, and turned them over to Virginia authorities to be tried for treason.
He was quickly tried and sentenced to hang on December 2. - See more at www.ushistory.org.
For further reading, see History.com's John Brown’s raid on Harpers Ferry.