The war, as such, was not directly caused by slavery. It was caused by the refusal of Union states to accept secession and by the CSA’s attack on Union troops.
Secession was mostly caused by a desperate desire to defend the institution of slavery, though as with any other movement other things were mixed up with it. The point is that every one of the other issues could have been compromised.
Slavery could not be, since the South demanded federal protection for slavery in all the territories as their minimum demand, while the Republican minimum position was no expansion of slavery.
Since the war was started by the insurrection, refusal to accept the insurrection was not the cause of the war. The people that started the war were in favor of the insurrection.