It was a states rights issue...the right of those states to own slaves. If you read the articles of succession for each of the confederate states (the actual words the actual people who decided "screw that Union thing..." put on paper to justify what they are doing and sent to Washinton), every one of them explicitly states "we are doing this because you are threatening our right to own slaves". This is the "well ackshually..." argument used to pretend the Confederates were fighting a noble cause and the rest of the hypocrisy being shoveled about.