To be pedantic, my nationality is American though I have mostly English and German ancestry.
I get the interest in genealogy, my mom is really into it, but it really rubs me the wrong way when Americans (I’ve only even encountered Americans that do this) talk about being “Irish” or “German” because of some ancestry. If your family has been in a the US for at least 3 generations, you’re nationality is American. Even ethnicity only counts up to about 3 generations of interbreeding, so I can’t even say I’m ethnically English only the closest is Western European. Granted, there are valid sub-cultural groups you can claim membership in such as Irish-American or Italian-American, but that isn’t your nationality or even ethnicity (both examples fall under Western European). I don’t mean to be too down on this thread, but generally this kind of attitude tends to go hand-in-hand with othering minority ethnicities and to the extreme: white supremacy.