DiogenesLamp: "Yes, but virtually all the imports in payment for Southern exports came back through New York.
The businesses of New York acquired about 40% of all the value produced by Southern exports, and Washington DC's cut of the money was also taken out there."
OK, first of all, when you say, "New York" what you mean are individuals who sometimes lived in New York, who allied with Southern planters economically & politically, Democrats, to exercise political control over the "DC swamp", from 1801 until 1861.
Second, your claim NY "acquired 40% of all value produced by Southern states" is just cockamamie.
That's because imports landed at NY warehouses remained untaxed until sold & shipped across the entire country.
Sure, New Yorkers earned warehousing fees, and Washington collected their tariffs, but those were far from 40% of the entire values.
The claim of "40%" represents an altogether different set of calculations.
DiogenesLamp: "New York virtually controlled all Southern exports to Europe.
I didn't understand this when I first started learning about this business, but in the last three years, i've read quite a lot of information which shows New York was running virtually all the trade occurring by way of the Atlantic ocean."
First, it would probably be fair to say: in 1860 Southerners did not build or own most of the ships which transported cotton to Europe.
On the other hand, to claim that anyone not from a Cotton South state was a "New Yorker" is pure foolishness.
Half of US cotton exported from New Orleans alone, another 25% from ports like Mobile & Savanah, and all those had entrepreneurs capable of financing & shipping US exports.
What they lacked in the South were customers for European imports.
Those could only be reached nation-wide from the railroad, sea & river transportation networks centered on New York.
And this is clearly a big, big problem for Lost Causers like DiogenesLamp, but there's no evidence it motivated Fire Eater Southern Democrats in 1860.