And no he's not. He's completely correct. He was reading the economic data. I'll say it again. WHERE THE SHIP LANDS IS IRRELEVANT. Do you think the city of Long Beach consumes vast amounts of goods from China? Duh. Of course not. That's just the single biggest port (by far) where most of the goods land. They are then trans shipped all over the place.
Nobody is saying 3/4s of their customers were in the South. Nor would they have to be. The goods were sold everywhere.
Why didn't they just ship directly ie from Southern ports to Europe and vice versa? Because that's not the way shipping/trade was organized. Because it was more economically efficient to have a central distribution hub then just as it is now. I might add Cotton was seasonal while other goods might not be etc etc.
Do you really think you....160 years later....understand how their economy works better than all those people at the time did?
And today, we have rail roads, interstate highways, and air cargo planes that can move stuff across the country. Not so much of that back then.
This was it

As I’m sure even you can see, there was not a lot of ways to ship stuff South via rail. And that’s not even factoring the changes in rail gauge that happened in Dixie. Like I said, if 3/4 of your “sales volume” were in the South, you would need to be a moron to ship so much to New York City. Do you think those guys were morons?
What economic data is he reading. Show me the data that says the South paid 75% of the taxes. Where is this wonderful data?