It is bizarre revisionism. They way you describe it being about slavery, one would never guess that Slavery would have remained legal in the Union if the South hadn't left.
How can you say it was a fight over slavery when both sides had legal slavery? The Union didn't even give up slavery until December of 1865; Six months after it had been eliminated in the South.
If the Union launched a war to destroy slavery, they should have started in Maryland, where they already had their armies.
Stop the revisionist history.
You’ve been told this before several times on numerous threads. The only way that slavery could be ended in the north was through the amendment process. Lincoln was not a dictator and could not just unilaterally end slavery. He did however encourage congress to write and pass such an amendment which did end slavery in the US.