It was most about treason against the United States.
There was no treason against the United States, because there was no law against a state from leaving the Union in 1861. That is one point that is very wrong, in my understanding.
If all powers that were not reserved for the Federal government were within the perview of the states, then the authority to leave the Union was entirely within the right of the state.
Is your wife betraying your marriage when she opts out because you abuse her? It’s the same idea for a state, when it’s being abused by the federal government.
I know the Founding Fathers did not want states to leave the Union, but their unwillingness to put that down in writing meant they recognized a state could leave if it wasn’t working out for them.