This ethnic/ancestral type reflects, presumably, Americans who no longer know, or no longer care, about the various derivations which contribute to their family trees. They’ve become a modern, generic homogenized ethnicity – the American-American.
I suspect I’m close to joining the American-Americans. I’m a little hazy on my family tree, beyond the knowledge that I’ve got some German, some Welsh, some Scottish and English progenitors. With such vague, and diverse, roots, simply calling myself “American” makes more and more sense to me.
Link to the full map & tool: https://public.tableausoftware.com/views/supercensus/AmericanAmericans?:embed=y&:display_count=no