There is another aspect that we have not taken for account. Promoting someone out.
This has been done in the military for so long, in which there is a "bumbling fool" that gets on a supervisor's nerves. The easiest thing to do in order to get rid of that person is to promote him/her out of their office.
Now of course I have never seen a black person go through that, so I am sure that racism is still a factor.