US South (without whites) ISOT from 1860 to 1000 BC

  Their probably going to be the great power for the foreseeable future.  Expansion across N America is almost certain and probably a lot more of the Americas while disease, even without any hostility from the blacks, is going to devastate the local populations. 

  They have a very wide range of crops and animals to work with, along with knowledge of iron-working at a level far more advanced than anywhere else in the world.  Also access to railways, steam engines and the like.    Furthermore I assume that libraries and other such facilities have come along as well so they will have those to maintain and expand upon their own personal knowledge.

  Its likely there would be some chaos at 1st as they adjust to no longer having masters and probably some internal power struggles as groups seek to gain power. 

  Ironically cotton is probably going to largely disappear as a crop.  There's no real market for it nor I believe any real capacity for refining the raw cotton and converting it into goods.  Some production is likely to be maintained for when factories can be developed for processing it after which its possibly an export crop of some potential.

  One other factor is that most of the slaves are Christians, excluding some recent arrivals and fairly devout, a millennium prior to Christ actually living so that is going to cause some interesting results.  Provided there's not a very strong reaction to 'the old masters religion' which is unlikely I think and this change could be seen as a miraculous deliverance.  True they won't realise the date at 1st but when they make contact with the old world both sides are going to have huge shocks.