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It has quite a few seeds of truth. 11 Southern states wanted to secede from the US, which would have made the Northern states collapse (because the South was exporting huge amounts of food to the big cities in the North), so Lincoln needed to weaken them.
Lincoln's move to set the slaves free in 1863 was exactly that, it was to undermine the South during the Civil War. The Northern states had slaves too, but the Southern ones directly depended on them, and it gave a good narrative about what the Civil War would "actually" be about.
The Midwest was the bread basket at that time. The South was mostly cash crops. The South also couldn't support themselves because they had no industry. That's why Britain and France didn't support them.
By the Civil War slavery was outlawed in Northern states.