Slavery was a major cause of the war.
However, abolition did not become a major reason to conduct the war until the Emancipation Proclamation.
There you go!
That makes no sense, How can slavery be a cause of the war if it as not at issue until long after the war started?
From the southern perspective the war was about preserving their freshly declared independence.
From the northern perspective as this act clearly demonstrates the war was about forcing the south under a corrupt union it no longer consented to.
Where is the slavery issue when the first shots are fired?