Wasn’t the war actually triggered by an attempt to enforce the ransom, aka import customs tariffs, on the South by the North? From what I heard, the slavery thing was a rather distant secondary concern.
The earlier war against England started for pretty much the same reasons - England first made unreasonable customs tariffs, then nobody complied, then they started to enforce them, then everybody got pissed.
One of the sources: Peter Andreas - Smuggler Nation - How Illicit Trade Made America.
