"I believe the Deep South "saw the writing on the wall"---a northern-dominated government---and chose the path to secession."

You see that is where modern day hindsight from which we draw the wrong conclusions, leads us to forming our perceptions. Sometimes those perceptions do not correspond with historical fact. Perception is not history, facts and events are history. The federal government of 1860 did not have the authority to impress it will on the States at that time. That type of Federal government which we live under today, is an outgrowth of the Civil War.

Lincoln did not win his election with a Majority of the votes. He was simply the largest vote getter in a field of three. The Majority of the people in the United States voted against Lincoln and the Republican party and the majority of the United States Congress had the Southern States remained in the Union. The Congress would have still been Majority Democrat which were Pro Slavery for the most part.

Even after the Southern States withdrew their Representatives the THEN Republican controlled Congress did not pass any meaningful anti slavery legislation during the entire 4 years of the war for fear of driving away the slave holding border states that had remained in the Union. And even more so if you will look at the voting records of that Congress fully 1/3 of that Congress opposed any reform even of the laws then in effect such as even the 13th Amendment. Which means that the "Republican" Control of Congress is a myth IF the Southern States had remained in the Union.

In fact driving the Southern States away may have been a part of a Larger Republican/abolitionist plan.

Since Lincoln was not even on the ballot in the South in 1860, I can see where the southern states would have just become fed-up with the whole federal process and figured that the best way to fix the problems was to abandon the old system, start over and let everybody (state) go which ever way they wished.

That to me would have seemed under those conditions to have been a very reasonable course of action. When something can not be fixed throw it away and get another.

The War started not because of slavery, but because Lincoln would not let the Southern states leave in peace. So why couldn't they leave in peace as they planned?

There was no holding authority in the Constitution that said they had to stay and couldn't leave if they wished. It was Lincoln that said they couldn't leave. And if it had not been for Lincoln there would have been no War.

So Slavery was not the Cause of that war, Lincoln was!