In the united states, most people practice they marry people who come from the same social class, racial/ethnic group, religious affiliation, and other categories considered important within their own social group.

This is endogamy. It is the practice of only marrying on your own group. This is a very common and extended practice, related to the belief that marrying someone with a similar personality, identity and beliefs will lead to an easier understanding, and a better marriage that marrying outside of it

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