In September 1997, during the process of revision of racial categories previously declared by OMB directive no. 15, the American Anthropological Association (AAA) recommended that OMB combine the "race" and "ethnicity" categories into one question to appear as "race/ethnicity" for the 2000 US Census. The Interagency Committee agreed, stating that "race" and "ethnicity" were not sufficiently defined and "that many respondents conceptualize 'race' and 'ethnicity' as one in the same  [sic] underscor[ing] the need to consolidate these terms into one category, using a term that is more meaningful to the American people."
How did racial categories appear in the US 2000 census?
race/ethnicity