Even if its not- it should be legal.
Just saw this argument:
“The South seceded. That made the war necessary. The South could have just peacefully remained in the Union.”
AKA: My wife wanted a divorce- that made beating her necessary. My wife could have just peacefully remained married to me.
Abraham Lincoln saved the union the same way that an abusive husband saves his marriage- by saying you aint going nowhere, bitch.
This is the best article I have found on the issue:
https://medium.com/politicoid/constitutionality-of-secession-19ce11c3b671
Very well reasoned. But secession is utterly impractical now anyway. In the 1860's, our infrastructure and societies weren't nearly as intermingled as they are now.
Now, we are truly a melting pot. Power grids, food supplies etc. totally blended. And separating the ingredients doesn't tend to go well. Even if it were possible, it would leave us with a leftist nation on our fucking doorstep, and this is not a good thing.