Well, other than the fact that they were in rebellion against the duly constituted government, and were trying to rip away nearly half of the republic's territory, and had raised a substantial army to attack the legitimate government.
The South was not going to invade. Later? Yeah, it's sort of what you have to do when you go on an offensive in a f***ing WAR.
It's what you do when you're an insurrectionist who is losing the insurrection and you're getting desperate, so desperate that you're willing to throw all the chips on the table for a final roll of the dice.
For a guy that can't get more than the word "slavery" out of the Declaration of Independence, I do not see any point in once more directing your attention to the primary purpose of that document. I fear a higher level of understanding is simply beyond you.