My understanding matches that of JB's. I recently read Steve Ambrose's Undaunted Courage, a biography of Merriweather Lewis of the famous western expediton. Apparently, Lewis was a well-to-do plantation owner before he got into the army, a fact I didn't know. Anyways, Lewis' money was all tied up in land & slaves; cash, stock, etc was virtually zero. So, though Lewis had lots of assests, he had almost nothing liquid. According to Ambrose, this was common. When a landowner died, provided he had enough land & slaves, his widow could sustain herself by gradually selling them off.
I kind of assumed that this pattern applied to southern mid-1800's America too. So it seems to me to have been a struggle for balance of power between two different economic systems carried out in the territories, with slavery as the main political football that kept the two sections of the country at loggerheads.
For Lincoln to have won a southern state, I suppose that would mean that there wasn't that much sectional mutual animosity, and therefore secession would never have occurred.
My "what if" about the 1860 election has always been what if Lincoln had been opposed by just one other candidate, say Breckenridge or Douglas only. Would Lincoln still have won?