"American" Ancestry

Out of all the maps I looked at this one by far interested me the most. This is a map of the United States by county and state, identifying the largest ancestry groups in 2000.  To my surprise the largest was German and after doing some digging I found that at one time (prior to WW2) German was seriously being considered as a primary language instead of or in addition to English. The Midwest also has some smaller pockets of predominantly Norwegian, Dutch, and Finnish ancestry.  However, as was the case with many later immigrant groups from Europe, people tried to assimilate and fit in, and often times rejected their native languages in favour of English so as not to appear any more foreign than they had to, and so that they would not be considered outsiders.  Often immigrants would purposely not teach their children the language of their homeland, preferring the children to only speak English. I find the counties (mainly in the south-eastern states) identified as having “American” ancestry to be thought-provoking.  Americans did come from somewhere else, except the Native American Indians (who also came from somewhere else, but a very long time ago).  Does this mean that the self-identified “Americans” don’t know where their ancestors came from?  Or does it mean that they feel they have been in America for so long that they are entitled to say their ancestry is all “American”?  

However,  if you combine all the British groups (English, Irish, Scots, Scots-Irish, Welsh) and the people who ARE of that heritage who should have checked that off instead of “American,” British would be the largest ancestry group.  I think this is intriguing as this could mean that many Americans don’t really know where their ancestors are from or don't even care where their ancestors are from because they only identify themselves as being simply "American".