War aims change as the prospects for winning or losing change.
The Confederacy was formed to preserve slavery. There wouldn't have been a war if there were no slaves.
By 1864 it was clear to Confederate leaders that they were going to lose the war. Losing meant they would face charges of treason and insurrection--potentially hanging offenses. It is not surprising that these leaders would grasp at any option for evading that fate.
It is also not surprising that few slaves would sign on. By 1864 most slaves could see that the Confederacy was losing. Why would they enlist in a losing cause for a government that had previously enslaved them.
Even losing the war, the South did its best to subjugate Blacks as soon as the reins of power passed back into white supremacist hands after the end of the Reconstruction period.
I don't think this book "proves" the war wasn't over slavery.
"Even losing the war, the South did its best to subjugate Blacks as soon as the reins of power passed back into white supremacist hands after the end of the Reconstruction period."
Blacks did not exactly have it easy in the North either, however. Let us not forget that fact.
Booth, Stanton, Johnson and Grant; the men who changed the aims and outcomes of the war from those envisioned by Lincoln.
How different history might have been.
That obviously doesn't mean that every southernor who fought was motivated by a personal desire to retain slavery. But if the Confederacy had fred its slaves at the same time it declared itself a separate country, there might not even have been a war. And certainly, the South would have gotten international recognition early on absent slavery.
Perhaps you should study a little of history. Are you aware that in 1832 the federal government sent warships into Charleston harbor and that it had nothing to do with slavery. It had to do with "nullification" theory. The South was extremely upset and ready to fight over the preferential tariffs. Had a compromise not been reached that year, the war of northern agression would have been fought 30 year earlier than it was.
With that said, slavery was an important component of the war. To deny that is to deny the writings of the men who fought the war. However, I think of it as the spark that set off the powder keg. The civil war was going to be fought, slavery was the spark that set it off. In 1832, the spark was tariffs, but the federal government managed a compromise to put out the fire before it exploded. In 1861, they couldn't put out the spark.
Only one minor correction: The Confederacy was formed to preserve and 'extend' slavery. The Southern states wanted slavery to be acceptable practice in the new territories. The North was against this in general.
The problem for the South, the mostly agrarian section of the country, was that they were trying to defend and extend a dying institution at the beginning of the Industrial Age, and went to war with that portion of the country that was perfectly suited to embrace industrialization. Too much bombast when cooler heads should have prevaled.
That is true of every armed conflict that has ever been and will be.