It is true that most of the black soldiers in the Confederacy were slaves who were fighting with their masters. However, there were many free blacks living in the South at the start of the Civil war, some of whom voluntarily enlisted in the Confederate armed forces. To deny that this well-documented, albeit minor, fact occured is historical revisionism and political correctness run amok.
I am perfectly happy to admit some (a few) free blacks probably enlisted and served.
They did so, of course, despite the official CSA policy banning them from doing so, which wasn’t changed till the last month or two of the war.
The official ban seems more relevant than the fact that some fought in defiance of that ban.
This whole argument comes down, as the article says, to the old straw man argument presented by both sides.
“The war was entirely about slavery” is one side.
“The war had nothing to do with slavery” is the other.
Both are so self-evidently false that one hardly knows where to begin in refuting them
The core issue in the rising friction between the states was slavery and its containment or expansion. This is just an indisputable fact. Anything else could be compromised.
So the issue of slavery led directly to secession, as most if not all of the seceding states said very plainly in their Ordinances of Secession.
At this point we have seceded states. It would have been theoretically possible for the states to have left without war, though given historical precedent not very likely.
Did Union loyalists resist secession primarily because of slavery? Of course not. They stated very clearly and repeatedly they fought to preserve the Union.
Did most southerners fight primarily to protect slavery? Equally of course not. They fought to protect their homes, property and families. Duuuhhh.
So the “Did slavery cause the war” issue comes down to semantics.
Slavery caused secession.
Had nobody resisted secession there would have been no war, and the resistance did not (especially at first) have much of anything to do with slavery.
And most southerners did not so much fight intentionally or conciously to protect slavery as to protect their states and homes.
Slavery caused secession. Secession caused the war. But few of those who fought were doing so for or against slavery, as such. Wars and human motivation for fighting them are complex.