I think you should check out the FAQ part about causes of the Civil War to get a better understanding of it. Let me quote /u/AncientHistory here as well, who put it succintly yesterday:

There absolutely were many Southerners that opposed slavery. There absolutely were many Southerners that opposed the Confederacy. Every state in the Confederacy sent troops to join the Union Army. Yet the fact remains, that the presiding cause of secession itself was slavery - and that every soldier that fought for the Confederacy, whether they owned slaves or not, whether they were from the Confederate states or not, whether they believed in the institution of slavery or not, fought for the enslavement of human beings. The Lost Cause was the cause for the continuance and furthering of slavery; the independence of the Confederate states was independence to continue slavery; the freedoms that they felt were denied to them were the freedoms to continue to keep others as slaves.