On May 21, 1856, Henry C. Pate participated with a posse of 750 pro-slavery forces in the sacking of Lawrence, which destroyed the Free State Hotel, two abolitionist newspaper offices and their printing presses. They also looted throughout the village. The next day, Congressman Preston Brooks from South Carolina physically attacked Senator Charles Sumner of Massachusetts in the Senate chambers with a cane. He continued hitting after the senator was bleeding and unconscious. After that, a band of men, led by John Brown and comrade Captain Shore, executed five proslavery men with broadswords at Pottawatomie Creek. Brown's men let Jerome Glanville and James Harris return home to the cabin of Harris. This incident became known as the Pottawatomie Massacre. Following the massacre, three anti-slavery men were taken prisoner, including two of John Brown's sons.
On June 2, 1856 Brown and 29 others met Henry Pate and fought the battle of Black Jack. This started after Brown's two sons were captured and held prisoner by Pate. The five-hour battle went in Brown's favor and Pate and 22 of his followers were captured and held for ransom. Brown agreed to release them as long as they released Brown's sons.
Some historians consider the Battle of Black Jack to be the first true battle of the American Civil War. The “official” event that is cited as the beginning of the war is the attack on Fort Sumter in Charleston, South Carolina, by Confederate troops on April 12, 1861.