How did people become identified, historically

Explore the meaning of identity politics. Consider, for example, the following questions:

How did people become identified, historically, as heterosexual or homosexual (note that these specific distinctions were unknown until the latter part of the nineteenth century)? How have people become pegged, as it were, to their ethnic group? (Note that St. Augustine in the fourth century CE may have been “black,” that is, Afro-Roman; it would not have occurred to the Romans to mention his “ethnicity.”)

Speculate as to why these distinctions are so important to Americans. What do they say about American culture?