Ethno nationalism says that our group of people are much superior to another group, therefore it is a birthright to exploit the perceived inferior group.
This goes for a group of people in a country, it works because it reinforces biological goals that we have. Our main biological goal is to first grow, get more fit in mind and body, reproduce and transfer our knowledge and wealth to our younger.
This means that from a biological perspective we put family first. In an environment of multiple ethnicities, it's easy to unite one ethnicity against the other. Because the ethnicity would feel that other ehtnicities are foul, and would dillute their bloodline / offspring, maybe deceive them. So social cohesion decreases with multiple ethnicities.
But back to the families, eventually you will get people who take it as far as being from a richer / higher status family makes him or her superior. That might also be the case if the family with status and power practices ex communication, eugenics and transfers wealth + knowledge to the next generation. Which is kind of what the elites are doing, they take this very seriously.
Elites from royalty in the past took this very seriously as well. The problem with royalty was the problem of succession. Greed would play a huge role in the off spring when it came to succession since the king / emperor had the decision making power. This structure would successfully prevent a royal bloodline from ruling too long. The real elites are in a far better position if not too much in the picture along with having a strong cohesion in the family so that they do not turn on each other to preserve their wealth + knowledge and with that, power.