What was the major issue that led to the civil war

"neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the united states, or any place subject to their jurisdiction." - the thirteenth amendment to the united states constitution, 1865 which statement describes the effect that the thirteenth amendment had on american society? a) male freedmen were given the right to vote. b) slavery was made illegal in the united states. c) ex-slaves were given united states citizenship. d) southern states were no longer allowed to use convicts as labor.