Jeez, can you not let go of it? Lincoln himself opposed slavery but he had absolutely NO PLANS to end it when he was running for president or after the war started! How could the PRIMARY reason have been slavery when Lincoln had no plans to end it?
Lincoln's plan was to limit it and stop its growth.
This is something that the South would not accept.
Lincoln wanted to return to the original intent of the Founding Fathers to put slavery on the path of extinction.
The South believed if slavery did not grow, their way of life would die along with it.
Slavery was the issue that led to the Civil War.