I remember talking to my granddaddy about the war. He had known many veterans when he was young. I posed the question to him “What if we had left Fort Sumter alone?” He was really stumped. He was a retired Army general so he certainly knew the military. We ended up writing down several scenarios. I wish I had kept them. He thought finally that there was a decent possibility that cooler heads might have prevailed had the South just waited it out.
Re: “What if we had left Fort Sumter alone?”
I think we had an economic alternative, too.
Lincoln could have offered to purchase all the slaves.
Obviously, there would be huge down stream problems still to solve - where do they live - are they voting citizens, etc.
But the cost of the War was many, many, many times more expensive.
Bottom Line - I do not think the Civil War would have happened once the issue of Slavery was removed.
The eventual solution - the total destruction of the Southern states, and the uneducated freed slaves left to live among their former owners - was incomprehensibly stupid.