The relative unimportance of slavery as a cause for war was made clear by Lincoln himself during his campaign for the Presidency in 1860, and he repeated that message in his first inaugural address:
Apprehension seems to exist among the people of the Southern States that by the accession of a Republican administration then- property and their peace and personal security are to be endangered.... I have no purpose, directly or indirectly, to interfere with the institution of slavery in the states where it now exists. I believe I have no lawful right to do so, and I have no inclination to do so.
Even after the outbreak of war in 1861, Lincoln confirmed his previous stand. He declared:
My paramount object in this struggle is to save the Union, and it is not either to save or destroy slavery. If I could save the Union without freeing any slave, I would do it; and if I could save it by freeing all the slaves, I would do it; and if I could do it by freeing some and leaving others alone, I would also do that.
It may come as a surprise to learn that, by strict definition, Abraham Lincoln was a white supremacist. In his fourth debate with Senator Stephen Douglas, he addressed the subject bluntly:
I am not nor ever have been in favor of bringing about in any way the social and political equality of the white and black races -- that I am not nor ever have been in favor of making voters or jurors of Negroes, nor of qualifying them to hold office, nor to intermarry with white people; and I will say in addition to this that there is a physical difference between the white and black races which I believe will forever forbid the two races living together on terms of social and political equality. And inasmuch as they cannot so live, while they do remain together there must be the position of superior and inferior, and I as much as any other man am in favor of having the superior position assigned to the white race.