The Kansas-Nebraska Act of 1854 really lit the fuse of the Civil War. The measure allowed citizens in those territories to decide whether or not to allow slavery.
Pro-slavery and abolitionist settlers raced into Kansas, trying to influence the vote. And instead of civil debate, violence broke out. Pro-slavery forces ransacked the town of Lawrence in May 1856. A few days later, John Brown (photo) and his followers massacred five pro-slavery men at Pottawatomie Creek.
In all, an estimated 59 people died in “Bleeding Kansas” between 1854 and 1859. Of course, even more died starting two years later.