My wife and I had genome testing done, part of that included ancestry stuff. Results were really interesting.
Interesting because my dad did some genealogy a few years back. Traced his family line back to the civil war before he lost track (sure, log into ancestery.com and you can see that someone has traced any family tree back through the time of Moses, but without any degree of accuracy) . Anyway, that means, basically, that I am American. There is no recorded history of my family's immigration to the united states for any of my 4 grandparents, because it happened to damn long ago and whoever they were weren't rich enough to have their names recorded somewhere.
On the other hand, my wife's grandfather immigrated from Italy, we we're talking 2nd generation immigrant right? (or is that third? whatever, you get it).
Results? I'm >60% Irish. The rest is German (like 20%), and "unspecified northern European" - because some genetic markers are less descriptive than others. Also, <1% native american - a verification of my grandfather's crazy stories of being 1/8th native american because of a bastard son of some person etc. etc. grandfather ramblings.
My Wife, <25% Italian. She was so pissed

. The rest was mostly unspecified southern Eropean, but also an appreciable amount ashkenazi jew - totally a surprise.
To me, this goes to show you how irrelevant your 'ancestry' is, and how unrelated it is to nationalism. Genes don't care, and they don't make nice pretty 50/50 splits when you make a baby. If you want to identify as German or Irish or Italian or American, fine, but know that your genes more than likely don't support it. Besides, even if they did, would it matter? People aren't dogs, we don't breed 'pure' bloodlines. Identify as you will.