First of all, to say that there weren't other concerns involved is to set up a straw man, but yes, it was mostly about slavery. Secondly, the Manchester Union Democrat doesn't say that secession was about tariffs and not about slavery. They aren't saying that the North is taking advantage of the South. Check out the link. Their argument is just that Manchester is dependent upon cotton and the North ought to conciliate the South and prevent a complete break.
I missed the Horatio Seymour quote. That is also not an "admission contrary to interest." Seymour, the "White Man's Candidate" for president in 1868, was trying to rebuild the Democratic Party. He didn't want Black enfranchisment. He wanted and needed those Southern Democrats in Congress to rebuild his party and take it to power. He was acting in accord with his party and his own interests and ambitions, not admitting anything that would hurt them. The tariff wasn't going to come down in 1866 because of the necessity of paying off the war debt. Seymour really should have known that, but instead he was playing politics.
You're at least willing to concede there were other significant issues involved. The usual PC Revisionists on here can't even bear to admit that. As to your claim that it was "mostly" about slavery, everything in the article belies that. Their entire concern was about economics and they couldn't have cared less about slavery - urging conciliation on that issue. That by the way, was the position of the Lincoln administration. Thus the Corwin Amendment. No the Manchester paper did not admit the Northern states were exploiting the Southern states (though they were). But they did admit that what really mattered to the Northern states was the money - not slavery. The fact that the original 7 seceding states turned down conciliation over slavery in order to pursue economic independence shows that the economics and not slavery were what was most important to them. The Upper South of course seceded over the constitutional issue of using force against another state for seceding - again, not over slavery.
x: I missed the Horatio Seymour quote. That is also not an "admission contrary to interest." Seymour, the "White Man's Candidate" for president in 1868, was trying to rebuild the Democratic Party. He didn't want Black enfranchisment. He wanted and needed those Southern Democrats in Congress to rebuild his party and take it to power. He was acting in accord with his party and his own interests and ambitions, not admitting anything that would hurt them. The tariff wasn't going to come down in 1866 because of the necessity of paying off the war debt. Seymour really should have known that, but instead he was playing politics.
You make the same mistake as BroJoeK in assuming Northern Democrats were somehow not Northerners....or did not represent Northern interests. They of course, did. Here Seymour is admitting once again, that THE key issue is Tariffs, not slavery or even the broader "negro question". Tariffs more than anything else divide North and South. The....let's face it....White men who lead both regions can sit down and bargain when it comes to Blacks. When it comes to the money however, they're prepared to fight.