On multiple occasions, Professor McClanahan made it clear that while there was a concern in the North around the spread of slavery in the territories, it generally was not due to the moral nature of slavery but rather about the political economy of slave states and their power in congress. If most Northerners did not particularly care about the plight of the slaves (even though they abolished the institution), why was that the vehicle in which they attacked Southern states? Why not attack agrarian economy or their anti tariff or anti internal improvements platforms? Why did we have so many compromises around slavery if that wasn’t the real concern by Northerners? Am I misunderstanding something?
I believe you almost answer your own question. After watching the lecture by professor McClanahan, the Northern States attacked the institution of slavery because it did give Sounthern States some more power and representation in the general government which, in turn, helped Southern States block many attempts by Northerners to pass more mercantilist economic policies. Anti-internal improvment/national bank/protectionist (tariffs) ideals wasn’t what gave Southerners more representation power it was slavery; so why attack the former three when it was the latter?
I hope that helps and makes sense.
Side note: Why the Southerners didn’t simply free the slaves and help them get on their freedom feet (yes, I just made that up and yes, it is very cheesy) so their representation would be legitimate and possibly on their side politically I’ll never know. But, then again, I’ll never understand the slavery mindset anyway.