What is an ethnicity?

[apie3000]

I actually have a hard time grasping exactly what the exact definition of an ethnicity actually is. Sociology differentiates between race and ethnicity by stating that race is about physical and genetic characteristics while ethnicity is all about culture regardless of race. That makes sense, but then why are ethnic nationalists so fixated on race rather than culture. Furthermore if I move to Japan, learn the Japanese language, convert to Shinto, and master the culture to the point that I am in practice more Japanese than the Japanese themselves but my ancestry is pure European and my skin white and hair blonde does that all of the sudden make me an ethnic Japanese? The Japanese certainly don't think so. Usually it seems that ethnicity is defined by both race and culture together however that makes no sense to me as those are two different things. I knew a guy that was a Hindu of Indian descent but spoke English as their only language and was as American in culture as I am. What ethnicity is he? So basically what I'd like is for someone to define ethnicity in a way that makes sense and tell me where that leaves me an American Southerner of European descent. What ethnicity am I and what ethnicity was the Indian fellow I mentioned earlier?

 

[firetown]

"Race" is only based on skin color or politics and artificially kept alive. And much of it is based on American history:
The settlers, the Natives, the railroad workers, the southern neighbors and the slaves.
There is no benefit in those separations, especially the "Hispanics" one which is made up and nonsensical.

Ethnicity to me is origin as in "all major parts of one's origin". Not simply the one that Europeans might visually "detect".
But again, this term as well has been perverted in terms of many nations with man-made cultural habits detesting a neighboring one. As we have seen in far too many discussions on this forum itself.