I've learned a lot about this in school, let me see what I can dig up...from what I can remember, it obviously has a lot to do with self-identity.
For starters, I take it you have not watched Obama's 'A More Perfect Union' Speech he gave.
It's long (37 minutes), but I'm sure you will find some bit of an answer to your questions.
Who is African American? - Wikipedia, the free encyclopedia