There is nothing in history to indicate that peaceful phasing out was going to happened prior to John Brown. Given the level of violence before he did anything, he was but a symptom and not a cause
There was a great deal of anti-slavery agitation that was going on in the northern states and especially in New England prior to the outbreak of hostilities between the north and the south.
John Brown was acting pretty much as an emissary of the northern abolitionist movement when he departed from his home state of Connecticut and went into areas like Potawatomie (sp?) with the intention of carrying out bloody massacres against innocent people.