In the united states and many other parts of the world, the common practice is for whites to marry whites, african americans to marry african americans, and members of specific social classes to marry within their class. this marital practice is called

This marital practice is called : Endogamy

Endogamy is a marital process in which the grooms and brides only limited from within local community or tribe.
This marital method is deemed to be out-of-date and only carried out in the past to maintain the 'bloodline' of a specific tribe or clan.