You make it sound like it was a great crusade to end slavery. Abolishing slavery was a secondary or even tertiary issue for the actual federal government. When Lincoln came to power in 1860 he only stated that he thought slavery was morally wrong and didn't want it spreading into any of the new American states and territories. Very little mention was made of those states where it was an established practise.
The overwhelming bulk of Union soldiers did not go to war to free blacks, they saw the real crime and rebellion as being secession from the Union. Most, like their southern counterparts, didn't give a rat's ass about the welfare of the blacks. Converesly the Confederates didn't go to war to make sure blacks remained in chains as property. Why was John Brown(captured in an operation commanded by Robert E. Lee), a militant abolitionist, condemned for treason, mere months before the Civil War? Why was Lee, a slave owner himself, offered command of the Union armies? US Grant didn't free his slaves, along with the other Northern slave owners until the 13th Amendment became law, on Dec. 18, 1865...two years after the Emancipation Proclimation? Grant also said,
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"If I thought this war was to abolish slavery, I would resign my commission, and offer my sword to the other side."
--- Ulysses S. Grant
And why did Lincoln say in his 'famous' emancipation proclimation
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,"I will say, then, that I am not, nor have ever been in favor of bringing about in any way the social and political equality of the white and black races ... I am in favor of having the superior position assigned to the white race."
and
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"I have no purpose, directly or indirectly, to interfere with the institution of slavery in the States where it exists. I believe I have no lawful right to do so, and I have no inclination to do so."
--- Abraham Lincoln, 3/14/1861 First Inaugural Speech
With the growth of factories, even the South saw the writing on the wall, slavery would eventually die out. Only about a 1/4 of the wealthiest farmers owned slaves in the southern states but until such a time as they could industrialize they saw slavery as a necessary evil.
Had the Civil War been about slavery, the Republicans would have issued an emancipation proclimation before hostilities even broke out, rather than waiting until January 1863. As it was the Union itself had slave states. Delaware, Kentucky, Maryland, Missouri and West Virginia were all Union States that allowed slavery. These 800 000 slaves were not freed by the proclimation(Sort of hypocritical if this war was all about slavery). They had to wait until local state and federal legislation was enacted(13th Amendment of December 1865). Only those slaves in the Confederacy were 'freed', by this act, in the hope that they would rise up and weaken the Confederate government and military.
No, it wasn't about slavery. Ending slavery played a part for some, but it wasn't the reason tens of thousands of Americans died in a bloody conflict.