It wasn't another nation. You are making up facts again. It was a rebellion. The rebels attacked the Union first. They started acting before Lincoln was even sworn in. They openly gave cause for their rebellion and didn't leave it up to the rule of law. They modeled their reasons off of the DOI, except they were defending their violation of the rights of people as opposed to protecting them.
Small but important difference.
I can sum up your post in two words:
Nuh uhn!
All you do is repeat the same horseshit over and over and over like a mantra. If that's what it take to salve your guilty conscience.
I'll list my pat responses to your bullshit talking points.
#1. Secession wasn't a rebellion.
#2. It doesn't matter why they seceded. Lincoln didn't invade Virginia to free the slaves.
#3. Ending slavery wasn't sufficient cause for invading a state of the union. It was legal.
#4. Kicking trespassers out of your territory is not an act of war.
In the future just refer to one of these whenever you indulge the compulsion to regurgitate your list of talking points.
Secession was a rebellion as established by them attacking the Union, not attempting to establish their secession legally but through force, and their own words when they seceded which leave no room for doubt that their leaving was going to be done with or without the laws say because they didn't need the rule of law just like the founding fathers didn't.
Yes it matters why the South left. It was their actions more than anyone one else's that lead to war. Their secession, their military action, their claims on the property of the Union, their raising of arms to resist the law, their fears of abolitionism, their desire to maintain slavery, their disregard for the lives of Union soldiers, their disregard for the bonds they created.
I am glad you finally recognize that one cannot invade itself. Lincoln was President of the Union and can't invade a state of the union. He can move troops within the union to put down a rebellion though.
Claiming territory with military force has started plenty of wars. Making a DOI like document can start wars.
Thank you for organizing your delusions so well. It is clear they all stem from the fact that you just ignore reality when it doesn't suit you and then use poor logic to come to silly conclusions.
Here is some reading for you straight from your heroes.
The Declaration of Causes of Seceding States