Wrong- the war was fought, because the North attacked-- PERIOD. If the North hadn't attacked, there would have been no war.
Likewise, the North did NOT attack to end slavery; rather, the North attacked in denial of state sovereignty and rights to secede; the South said the states had it, the North said they didn't.
Finally, the North specifically CLAIMED that the war was NOT about slavery- and Lincoln even compared slaves to pigs, in terms of what he cared about them and their welfare.
Therefore, slavery was merely the context of secession-- it had NOTHING to do with the reasons for the war itself, regardless of the reasons for secession.
And since when does secession, necessarily mean war? If both sides had recognized that the states had a legal right to secede, then discussion would have been over-- no war. Period.
The only time secession requires war, is when there IS a denial of such a legal right.
The war was fought over the LEGAL issue of state sovereignty, period.