Assuming the South did win......

[KG_SSpoom]

How would this have affected world history?
WW1 could have been very different......

[KG_Kharkov]

The U.S. never intervenes in Europe in WW1. The South's agrarian society eventually turns into an economic quaqmire. Although I've never read any of the novels, there is a whole set of alternative sci-fi histories premised off of this.

[KG_SSpoom]

I did read them and they are pretty good.
WW1 is fought also in the U.S. with the South allied with the British and French and the North allied with the Germans.
The books are by Harry Turtledove.