“With the Southern export value being 73% of the total, and the Northern export value being 27% of the total, it would be reasonable to assume that the Southerners were somehow paying for 73% of the imports”
You seem to assume that only exports paid for imports.
This is not the case. The South was not the only section of the nation to create wealth.
As an example: from the 1860 census, the value of manufactured goods from the State of New York $378,800,000.
Little of these manufactured items found their way to Europe. These manufactured items were sold all over North America. Maybe the manufacturers in New York had enough money to buy imports in the quantities represented by your Tariff graphic.
No, I clearly said that 73% (at least) of the imports were paid for by Southern produced goods, and 27% (at most) were paid for by Northern produced goods.
As an example: from the 1860 census, the value of manufactured goods from the State of New York $378,800,000.
How much of that value was the consequence of protectionist laws that caused the South to have to buy those products at the inflated prices at which they were sold?
What would have been the value of those products if European machinery had been purchased in their stead?
Little of these manufactured items found their way to Europe. These manufactured items were sold all over North America.
What would have been the consequences to these manufacturers if the South had opened up the doors to European versions of similar products to the entire Midwest regions?
You want to talk about a powerful incentive for Northern manufacturers to go to war? There it is.
Maybe the manufacturers in New York had enough money to buy imports in the quantities represented by your Tariff graphic.
Where did they get the money to buy European goods? Only 27% (at most) could have come from their own sales to Europe. Didn't the other 73% (at least) have to somehow come from Southern production?