Stephens notes as much in his speech.
It, however, was not the deciding issue that those like Delorenzo want to make it to be.
Slavery was that crucial issue that led to the final rupture between the South and North.
That isn't what the newspapers in New Hampshire and New York said. That isn't what Lincoln said!
"The crucial issue that led to the final rupture between the South and North" was the fact that everything went on the line, as the North tried to take the South to the cleaners and embraced a take-no-prisoners attitude in doing so.