Slavery was always just an excuse. Federalism was always the reason. In the last couple of months, I have come to realize that the cause of the war was money. The loss of huge amounts of it to North Eastern financial interests, and the acquisition of it by Southern Ports who would obtain a huge chunk of the European trade because of greatly lowered import tariffs.
Had the South succeeded in establishing trade with their stated tariff of 13% on imported goods, the Northern Tariff of 45% would be uncompetitive. Likewise the usage of NorthEaster shipping companies, Warehouses and textile factories would have gone a begging.
And Independent South would have been a devastating economic Hammer against the North East's financial security.
The war was started because they very badly needed to stop European Trade with the South. Allowing it would have wrecked the financial well being of the North East. This is why one of the first things they did was to create that Blockade. If the European powers had gotten a taste of normalized trade with the South, then they would have thrown their weight behind Southern Independence.
The war was in fact about money.
Here's a map to give you an idea of what was at stake from allowing an Independent South with lower import tariffs.
Had the South succeeded in establishing trade with their stated tariff of 13% on imported goods, the Northern Tariff of 45% would be uncompetitive. To who? Goods bound for Northern consumers would still have paid the 45% regardless of what the Southern tariff was. Good the Southern states used to buy from the north duty free would now have a 13% tariff on them.
Likewise the usage of NorthEaster shipping companies, Warehouses and textile factories would have gone a begging.
Why would Northern shipping companies have gone begging? What alternative to the Northern shipping companies did the South have? They had no shipping industry of their own. Why would warehouses go begging? If imports destined for Southern consumers arrived first at Northern ports they would not have been taxed. The Warehousing acts provided for that. No tariff would have been applied until they reached Southern ports. Why would textile factories go begging? Was the South going to go out of the cotton business? Why wouldn't they have continued to sell to Northern customers if they were paying the going rate?
And Independent South would have been a devastating economic Hammer against the North East's financial security.
I think you grossly overstate the impact an independent Confederacy would have had on the North. If anything it would have been the Confederacy who would have been at the mercy of the U.S. since Northern ships moved their cargo, Northern businesses brokered their cotton, Northern insurance companies insured their crop, Northern banks financed their plantations, and Northern manufacturers provided just about all their goods.
The war was started because they very badly needed to stop European Trade with the South.
Your own chart shows that there was very little trade between Europe and Southern ports.
The war was in fact about money.
Actually it was about slavery but hey, you'll never accept that.