Nationality and race and ethnic/Cultural background are different.
Nationality is: American, African, Italian, French etc., if you live in that country. It is the status of belonging to a particular country.
Race is: Caucasian, African, Asian, Indian etc. It is a classification... of peoples.... which may include genetic history or geographic distribution & history and may include, physical characteristics.
Ethnicity is: Irish, Japanese, Chinese, French, Italian, etc., ie: your cultural heritage as a group, that may have a common National heritage and cultural tradition.
My kids are Bi-racial. As is common in Hawaii. Many are multi-racial.
Mine are also bi-cultural ethnically.
Their Nationality is: American. This is where they were born and where we live.
My Husband is European.
I am US born and raised. But in Hawaii.
No, it does not define a person. It is a complement and their cultural background. And an identity. Not definitively though, as each person identifies with their ethnicity in varying ways. Then their Nationality.