Religion
In reply to the discussion: Catholic "criminals" [View all]Act_of_Reparation
(9,116 posts)Ethnicity can be determined with some degree of accuracy through Y-chromosome DNA haplogroups. This is very basic genetics. If a population of people lives in relative isolation over a period of time, they will exhibit genetic similarities.
For the purposes of biology, "ethnicity" doesn't really tell you anything about a person save for the geographical region from which his or her male ancestors emerged.
Nationality, however, is a social construct. I am, genetically speaking, of Northern European stock. I am not, however, Northern European by nationality. I am an American. I am a New Englander. I am a Connecticutian. So on, and so on.
It sounds to me like you are conflating ethnicity (bloodline), with nationality (cultural identity). The two are similar, but not interchangeable.