Lincoln prosecuted a war that was thrust upon him. He had little choice other than bow to southern aggression and turn over forts and facilities that belonged to the U.S. It was the Davis regime that turned to war to settle the matter, not the Lincoln Administration. So the question you should be asking was why slavery was worth launching a war over?
...attempt to generate a coherent (I know, it will be difficult for you)...
It appears from reading our posts that coherence is not the problem here. It's comprehension on your part.
"The time for compromise has now passed, and the South is determined to maintain her position, and make all who oppose her smell Southern powder and feel Southern steel" -Jefferson Davis, Feb 16th, 1861