I have noticed two African-American Caldwell ladies signing the guest book. It would be a great help if they could join in the debate as it is an area about which I know little. It will not be too much of a bore if I trot out what little I know:
I heard that there are a good number of African-American who bear the surname "Caldwell".
I also know that Glasgow in Scotland was the hub of the european tobacco trade for quite a long time. This was because it is just a bit shorter trip to Glasgow than to other port in the mainland of Britain. Furthermore the astute Scots probably tied up both ends by controlling the source of supply. There were many very wealthy "Tobacco Lords" in Glasgow and they possibly funded tobacco plantations in the USA. I would not like to venture much on the location of the plantations as I am sure that there are others who access this site who are much more knowledgeable on the subject. If I say "Virginia" I am probably having a reasonable guess. I presume that the African-Americans came to the Caldwell surname somehow through the owners of the plantations. Again I am not sure on how surnames were adopted in this instance.
I have not seen anyone claiming that Caldwell's were responsible for the situation where the African-American community adopting our name in what appears to have been a fairly extensive manner.
I believe that most of the cotton trade into Britain was stopped by the blockade of the Confederate ports in the American Civil War. There was undoubtedly trade in cotton into Scotland as well but I don't think it was anything like on par with the trade into Lancashire in England. This would not stop Caldwell's being Cotton Planters who traded back into England. During the blockade period alternative sources of supply were found and an alternative trade in sugar from the West Indies (Jamaica in particular) was started.
If you can help we will be glad to hear from you, if we can help please let us know. Its always best if you can contribute something of interest from your own research, family legend, or you own thoughts, rather than just asking questions - it just makes it easier to reply.