4chan

It depends on if you are speaking about ethnicity, the concept of race, or the diversity of genetics. I guess it also depends if you are talking about the percent of the total population, or just the total amount of ethnic groups living in the state.

America may be racially diverse, or have a large number of different ethnicities living in the country. But when it comes to ethnic and genetic diversity, it's pretty hard to beat just about any country in Africa.