IF the Civil War was fought over slavery (10% or fewer of southerners owned slaves), Lincoln could hardly have offered Robert E Lee, scion of a prominent, slave-owning family (Lee family plantation, Stratford Hall, was built by slaves), the job of running his Union Army.  IF the war was fought to free slaves, ol' Abe (clearly a white supremacist who wanted to deport freed slaves) would have issued the Emancipation Proclamation in 1861 when he provoked a bloody, horrific war, instead of cynically, in 1863, when he had been losing battles and firing generals.  IF the war was fought over slavery, Lincoln couldn't have advocated for the Corwin Amendment (a Constitutional Amendment) to make slavery "permanent and irrevocable."  Lincoln desperately wanted southern revenues to keep flowing North, disproportionately benefiting Yankees which is why the Constitutional Amendment, named for Senator Corwin, was so important to him- the Union, at all costs (600,000 lives).