As a researcher of Union regiments during the Civil War, I recommend you find books written by the men who were there, not the arm-chair historians of today. My area of knowledge is with the Union side of the Civil War, I'll let my "Southern" brothers vouch for their own thoughts. If you read the many Union regimental histories and memoirs, the Civil War was viewed as primarily about preservation of the Union. Though certainly many abolitionists served within the Union forces, ending slavery was not the reason most joined to fight. One Captain from a Wisconsin unit bitterly complained about Lincoln's Emancipation Proclimation, indicating that creating "Colored Regiments" only siphoned off supplies and support from his unit.
I'm happy to help you in any way possible if you'd like.