[BroJoeK]

SoCal Pubbie: "I don’t get this idea that the Navigation Act of 1817 was part of some Yankee conspiracy to enslave the South.
I’m doing a lot of research and it reflects part of what you alluded to. Companies weren’t all 'Southern' or a 'Northern' or even 'British.' "

The key fact here is that DiogenesLamp hopes to impose his own historical narrative on historical people who would not recognize it.
He claims they were being forced by law to use certain shippers or certain companies -- "Northeastern power brokers" -- when the fact is they weren't "forced" to do anything, but instead did what seemed at the time the best things to do.

Today the US has dozens of large ports, including inland ports like St. Louis (#19).
Of those, New York-New Jersey is number three overall, behind Houston and New Orleans.
New York at #3 handles roughly 5% of total US freight tonnage.
So there is nothing unique or monopolistic about New York today, nor was there in 1860.

[DiogenesLamp]

The key fact here is that DiogenesLamp hopes to impose his own historical narrative on historical people who would not recognize it.

The key fact here is that the economics of the situation clearly shows that New York and Washington DC were ending up with all the trade money.

Another key fact is that most of this money would have disappeared from their control if the South traded directly with Europe. They wouldn't get what they had come to regard as "their cut."

We have here a towering motive called "Money" but gullible people prefer to believe it had some other cause than that, though uninvolved observers on the other side of the Atlantic pretty much nail the cause as a dispute over money, nor morals.