Constitution wise it would have been wise of Abe and Congress too allow technology to make slavery as uneconomical in the south as it had became in the north. Likely by 1890 it would have happened. Automation would have taken over. That was why northern industrialist were so darn eager to allow it to be abolished there and demanded it be abolished in the south. These were at the time ruthless men who put money and power above everything including nation. They were pitted against each other and drug the nation to war. There was Oil wars, railroad wars, mining wars, etc all which lead up to The Civil War.
Smedley Butler's opinion on war was on the money in relation The Civil War. It was an economic war and later the reasons rewritten as political correctness took hold of schools in the 1930's on. The war did not change any prevailing racial attitudes. Even the military was segregated in WW2. The north did not treat free blacks well thus rioting happened after The Civil War. They received near slave wages at jobs others would not take. In the military same thing. Who do you think built the toughest stretch of the Alcan highway in WW2? There was more segregation likely in the north than south.
Economically slavery survived well into the early 1960's in some regions. Tennessee Ernie Ford's song Sixteen Tons was reality for many. So was the Company Store a legal form of slavery that flourished in the U.S. for 100 years after the Civil War. The New Slavery.
If you read anything of Lincoln, from his speeches, to his debates, to his inauguration address, to his proclamations, it was clear that he sought the peaceful resolution to the souths rebellion.
He was even willing to sign on to the original 13th amendment which would have defined perpetual slavery (a huge mistake IMO) in order to save the union. None of it mattered to the southern hotheads who were spoiling for a fight. We were fast becoming the last industrialized nation to continue the practice of slavery and increasingly the subject of hostility and alienation from other nations. Why do you suppose no other nation would stand with the confeds in their rebellion?
There was a winner in that painful conflict - The United States (and its Constitution). We are still here enjoying God’s bounty. If an improbable confed win were to have happened it would have set the scene for decades of warfare between north and south, and a thousand internecine conflicts within (and especially along border communities) of both nations. There likely would no longer be nations but revert to nation-states, prime for the picking.
No, the reason for the conflict that cost so much in misery and the loss of human life was the southern slaverocrisy who pitted farmer against farmer, neighbor against neighbor, and family against family so that they could continue to enjoy the finer things brought to them courtesy of the black man.