I've never really been sold on the slavery = non important thing; the simple fact that the southern states were so focused on keeping slavery makes it a major issue in their secession.
I don't have time to read the whole topic, at least not yet, but I'm a little wary of this. In terms of its collapse...slavery had been expected to "die" before the civil war even started, but cotton becoming a major cash crop of the south in turn revitalized the system. As far as it being in the north...is this addressing the slave states which stayed with the union and were (until the emancipation proclamation) allowed to keep their slaves?Slavery was a single issue, one that would have collapsed in about 10 years anyway, and an issue in the North as well.