This post has been significantly updated, with comments referencing the first version removed. Suffice to say, readers were not happy to see that we did not count African American as an ancestry. African Americans were not counted in the first version of this post because new Census material treats the group as a race, rather than an ancestry, and lists ancestry only for smaller groups from specific African countries. In the updated post, however, we decided to count African American as an ancestry as well.
As for controversy surrounding the use of ancestry versus ethnicity, let me note that these words are ambiguous and would arguably both serve to describe this list. Ancestry refers to "one's family or ethnic descent." Ethnicity refers to "the fact or state of belonging to a social group that has a common national or cultural tradition."