I am an American with a great deal of Irish ancestry. I have also been told we have a great deal of “Black Dutch” ancestry (I have also heard “Black Irish” used to describe this before), Scottish, French, German (which may actually be more Slavic “Wendish” ancestry), and Native American.
I did a 21-marker-pair autosomal DNA analysis through DNAtribes to get some clues. My results were strongest for Spain (with Basque as the highest of the regions matched) and Italy. This was followed with Russia, Ireland, Scotland, Macedonia, and Romania. My top 3 diaspora groups were Israel then Caucasian then Mestizo.
I am hypothesizing that my Irish ancestry may have been concentrated near one or more of the port towns with a long history of “contact” with Spain. Feel free to comment about this hypothesis and/or provide your own. There are many others out there that have “Black Dutch” and “Black Irish” ancestry out there that would love to hear reasonable hypotheses that might appropriately explain these terms.