Interesting moment.
The point of divergense, I think is 1803 - Napoleon refuses to sell Luisiana to US. What can be then - sooner or later Luisiana proclaims independance from France. So, Northern America will look like Southern - there are not one big state, but several small ones.
I am not agree with SurfNTurfStraha - there will not be neo-feudal lords have slave labor combines - slave will not work with complicated machines, remember the Roman times. And of course slavery will not survive until modern days. Confederacy can win the war and separate, but it today it will look more like modern Brasil, then XIX century Georgia...