Not an issue, the issue, regardless of how much our pro-Confederate friends wish to emphasize the Morrill Tariff & other matters.
Republicans like Lincoln were abolitionist enough to infuriate Southern Fire Eaters, even though the Republican platform only called for restricting the expansion of slavery into western territories which didn't want it.
The fact is that Lincoln was the first openly anti-slavery candidate to be elected President, and that was enough to drive Fire Eaters to first declare secession then war on the United States.