ethnicity: a population of human beings whose members identify with each other, on the basis of a real or a presumed common genealogy or ancestry, behaviors, beliefs, values, and symbols that they accept, generally without thinking about them, and that are passed along by communication and imitation from one generation to the next. the non-biological part is the decisive one.
citizen: a native or naturalized member of a state who owes allegiance to its government and is entitled to its protection
nation: nation may refer to a a community of people who share a common language, culture, ethnicity, descent, religion, or history
*"in general" to all