Nobody claims that Southern secession would have no negative affects on Northern economic interests.
But that is far from claiming that such interests were the cause of Civil War.
They were not.
The cause of war, pure and simple, was the Confederate military assault on Union troops in Union Fort Sumter.
Absent that Confederate assault, there would be no war, no "Anaconda Plan", no blockade of Confederate ports, none of it.
There would also be no secession declarations by Virginia, North Carolina, Tennessee & Arkansas.
Reason: from Virginians' perspective war was necessary for them to declare secession, and that's what Fort Sumter gave Virginians.
Other Upper South states had decided to follow Virginia's lead in first refusing to secede and then declaring secession after war began at Fort Sumter.
Rockrr is fond of listing all sorts of examples where Southern forces took over formerly Union installations and assets, but he/she never seems to notice that none of these were deemed sufficient to provoke a war.
Charleston was the primary port through which all European trade would flow. The reason it was a sticking point, is because *THAT* port represented the dire financial threat to the North. They simply could not allow regular and profitable trade with Europe to develop.
I do not think you are adequately counting the costs that allowing competing European trade (at low tariff rates) would have had on the economic conditions in New York, Philadelphia and Boston.
You may be aware that the first shots were fired by Federal troops on Florida civilian militia in the area of the old Spanish Fort San Carlos in Pensacola in January of 1861. The next day the Star of the West, a federal ship under contract to run supplies into Ft. Sumter received fire and retired from the area of Ft. Moultrie.
Following these events, nothing changed. No declaration of war, nothing.
The same is true of the firing on Ft. Sumter. The seceded states remained in place.
The only event related to a declaration of war was Lincoln's issuance of personnel call up and a blockade of Charleston. These commands were signed by President Lincoln on April 17-19, 1861, ordered the Secretary of State to affix the seal of the United States to his proclamation blockading the South, and thus made it official. Under international law of the era, declaration of a blockade is an act of war, and thus after the conflict the United States Supreme Court held the institution of the blockade to constitute the legal commencement of the Civil War.
No doubt you may be inclined to rely on your choice of historians for their opinions....the libraries and Google are full of them. However, for the purposes of consummation of war time issues, the United States government itself affixed the beginning on Lincoln's actions, with no transactional relationship to Charleston Harbor.