Is America a big melting pot that is full of little melting pots?

For example, white people usually only have children with other white people, however, they don't often discriminate based on country of origin, Germans, Irish, English, French, etc are mixing with impunity in this country and there are very few full bloods left. The same goes for blacks, they usually only mix with other blacks, however, the blood of a million tribes is over here and tribal lineage never factors in to the decision to produce children. The overwhelming majority of blacks also have white or native blood in them. So that's two melting pots within a melting pot. Hispanics are a melting pot for sure, they are mixture of white, Native, blacks, Asian, and more. Even Asians are in a melting pot in those country, they usually produce children with other Asians, but thy don't base their decision on country of origin, Chinese/Japanese/Philippino/Korean relationships are very common and are not deemed to be interracial relationships, but simply Asian with Asian.