Another reason is that Africans aren't educated on what blacks went through in America. Unless they live in South Africa, they are most likely exposed to racism. Maybe colorism, but not racism. It is not apart of the curriculum in African schools to learn about Black history, and why should they if it doesn't affect them? They learn about what's going on in their own country. Ironic how the system is set up so that we don't even get to properly learn about each other and much we are actually alike isn't it?
Instead of thinking of each other as "Blacks" and "Africans", why not think of each other as distant relatives. A quote by Maya Angelou says, "If you will have a person enslaved, the first thing you must do is convince yourself that the person is subhuman. The second thing you have to do is convince your allies so you'll have some help, and the third and probably unkindest cut of all is to convince that person that he or she is subhuman and deserves it." This is why happened to blacks when they were separated from their African relatives, only to be reunited years centuries later and not even be able to recognize each other. Just remember we all have the same blood running through our veins. That's what unites us.
Read more at http://www.brainyquote.com/quotes/quotes/m/mayaangelo
Please read these collection of tweets by @Luvvie on her website www.awesomelyluvvie.com. She describes the situation from her point of view as a Nigerian.