If you could make it work, one impact would probably be the introduction of both Islam and animist religions into the alternate United States. Maybe voodoo and its relatives would be significant religions, while Islam would be a well-established minority religion.
I'm not sure how that follows. From previous discussions I think it was agreed that if Africans were not brought across the Atlantic in chains, they probably wouldn't come as free laborers.
The early 13 colonies used black labour with a '99 year indenture' - basically life long slavery, but the children were free.
Have that be kept, especially given the rulings in England, and you could possibly avoid technical slavery.
This disappeared pretty quickly after the introduction of black slavery, though, didn't it?
There may
ways to severely limit slavery's development in the English Continental Colonies as late as the latter 17th Century -- this, after all, is OTL when the Colony of Virginia started to institutionalize the practice, and when the Province of Carolina, initially meant to be developed along ideas of John Locke, was first being planted. If Portugal loses the Restoration War and the English Restoration stopped or delayed, perhaps, and the Atlantic Slave Trade is hindered enough that the cost of importing slaves prevents these developments. If they are, then Georgia might even stand a chance of being a free colony.
In the future US, maybe, but not in the Americas in general. If the Spanish would be using African slaves, and making money hand over fist, all the other powers with Caribbean colonies would eventually use slave labor too. Greed is too powerful of a motivator. And really that would mean plantation slavery would almost inevitably move onto the British continental colonies too.
In my opinion for this to possibly work you would need a very early POD with a strong religious prohibition on slavery. The effects on the Americas would be massive. Since American Indians and whites died in droves in the tropics and sub-tropics, colonization there would be slow and those places would remain undeveloped. European colonization as a whole would be far slower and less profitable, though the Spanish would still benefit tremendously from their Central and South American empire and exile colonies of English and French people in the temperate areas would still survive and grow, albeit with less booming economic growth. Western Europe as a whole would be less wealthy.
But, African economies
not dominated by slave raids and the draining of their labor forces might have a thriving coastal trade in non-human goods, with trade with them possibly making up for some of that economic loss in Europe.