“Foreign shipping had to sail empty and this put them at a serious economic disadvantage compared to Northern shipping.”
No, they did not. Read post 873 for multiple examples.
To recap:
The reason for secession was the South’s desire to preserve slavery.
The trigger for secession was the election of Abraham Lincoln, which fed fear of the abolitionist foundation of the Republican Party.
The American Civil War began when units of the South Carolina Militia fired upon a Union fort in Charleston harbor.
Took a look. How much of a cargo did those items represent? Also, we know that some ships landed cargoes in Southern ports, but how much a percentage of the total trade do those cargoes represent?
A pittance i'd wager.