One tends to fight when fear is involved (fight of flight) the Slave states could not leave therefore flight was not an option.
There is a good LEGAL argument that the CSA or any state could succeed but when the State of South Carolina fired on Ft Sumter that was caucus belli.
Yep. Plenty.
"....but when the State of South Carolina fired on Ft Sumter that was caucus belli."
Seems a more prudent approach would have been to deal with South Carolina's indiscretions solus.