When the next civil war occurs, it will not be regional like the last one. It will be man vs. state. In the instance of Texas, it will be the people vs. the federal government, while in places like Indiana and Kentucky (where the state governments walk hand-in-hand with the feds and will probably back them) it will be the people vs. the state and feds. The general consensus of the US military is that they would not be reliable to the federal government for domestic war. There are too many in active and reserve duty now talking about this possibility. That is why the Federal government has and is training foreign forces for urban combat. They will need the help. They will lose.
You do realise that the civil war wasn't over slavery right. Also slaves existed in both the north and the south at the time.
I think it's over 100k now. Only 25k is needed though to warrant a response from Washington