Yes there was. It was in all the papers.
No. It was lawful secession, not insurrection. The states had every right to secede.
If there is no law that either allowed or prevented the act it can’t logically be “legal”. At best it could have been characterized as “extra-legal”. That they did so in defiance of the rest of the union showed their true illegal intent. And a Supreme Court decision put the question of unilateral secession to rest. For reasonable people at any rate.