This approach to rewriting history has been going on for more than a century. Alexander Stephens, former vice president of the Confederacy, published a two-volume history of the Civil War between 1868 and 1870 in which he hardly mentioned slavery, insisting that the war was an attempt to preserve constitutional government from the tyranny of the majority. But this is not what Stephens said in the great debates leading up to the war. In his “Cornerstone” speech, delivered in Savannah, Georgia, on March 21, 1861, at the same time that the South was in the process of seceding, Stephens said that the American Revolution had been based on a premise that was “fundamentally wrong.” That premise was, as Stephens defined it, “the assumption of equality of the races.” Stephens insisted that, instead, “our new [Confederate] government is founded upon exactly the opposite idea. Its foundations are laid, its cornerstone rests upon the great truth that the Negro is not equal to the white man. Slavery—subordination to the superior race—is his natural and normal condition. This, our new government, is the first, in the history of the world, based upon this great and moral truth.”
Read some of the writings from Calhoun before the war, Calhoun was still passionately pushing the same ideals that had led him to resign from the Jackson administration all those years.
The Northern troops called themselves Union as that is what they were fighting for. They didn't call themselves liberators or the abolitionists.
Same for the Confederacy. They were fighting to establish a new nation based on local sovereignty. That is why they called themselves Confederates.
The real start of the war is so plain a blind man should be able to see it. When Lincoln called for 75,000 volunteers there was no doubt what they were for. No one thought the South was going to attack the North. Fort Sumpter was in Charleston harbor, not Boston.