both were running for US Senate from Illinois, gave Lincoln national popularity, Lincoln argued against the spread of slavery, not the abolition
John Brown's Raid on Harper's Ferry, VA
John Brown, an abolitionist, planned a slavery uprising in VA, it failed and he was captured and hung. This event further separated the pro-slavery and anti-slavery sides.
The Election of Lincoln
Democrats were spilt between extreme pro-slavery and moderate slavery forces. When Lincoln won, the South seceded.