I’ll give you the best answer I can, having spent some time on this question myself.

  1. Nation states and empires attempt to crush local identities, or deny them. (china and mongols the most obvious). Governments have incentives to be dishonest. All government data is suspect. Unfortunately the Academy is a co conspirator to government because it is cheaper to use government data than to conduct genetic and cultural research.
  2. During the time of nation states, most europeans lost their local identities, although our ‘tribes’ at last at the macro level are still ascertainable in many cases. Even today, despite the fact that northeastern, northern, central, and southern descendants in the united states all come from different regions and tribes, and still practice those cultural differences, the government suppresses those differences.
  3. So when we say ‘ethnicity’ are we saying nation state, or race, sub-race, tribe, and clan, using the identity with which they identify themselves? For example, the french speak french, but and parisians are culturally parisian, but the french countryside is identifiably germanic and has retained those cultural tendencies. American whites are primarily german, but speak english. Southern italians are ethnically greek, and northern ethnically german. They know this, but data just groups them together.
  4. For these politicized reasons, I tend to think the only honest means of judging ethnicity is genetic, cultural, and linguistic in that order, which is how people tend to describe themselves if they have an ethnic identity that is important to them. For those that it isn’t there is usually a reason to avoid it and choose some else less ‘truthful’.
  5. Using that method of categorization, As far as I know there are four major races(with austrailasians earning their own category), nine or so subraces (separating out the various indo europeans in particular), over 100 minor races and a vast number tribes and unmeasurable number of clans.
  6. But the truth is that genetics is going to solve this for us within the next few decades and governments will no longer be able to play their games with us.

https://www.quora.com/How-many-ethnic-groups-are-there-in-the-whole-world