system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 - What people mean when they claim the Civil War was not about slavery. 

Ok - so I get that one of the main reasons for the Civil War was that the Confederate states were fighting for State's rights. But wasn't slavery the biggest State Right the southerns wanted to protect? Slaves becoming free would have put a huge dent in their cotton market because they would have to pay for workers. 

So why else do I see Confederate flag stickers that say "If you think this is racist, you need a history lesson?" 

Edit 1: Wow, I didn't expect such a great response. I will read through these Monday. Thanks to everyone. I have always wanted to be educated about this. I realize it wasn't something that can truly be a ELI5 because of it's complexity, but I still thought this was a great place to put it. Thanks, again!
gpt
As the north became more industrialized the south became more and more a one crop economy-cotton- which depended heavily on slave labor to be popular.  Balancing the needs of two such different economic systems became almost impossible especially as most of the newer states were free states.  So yes, it was about slavery, but more from an economic point of view than a moral one.