All Black people in America have at least a little White in their ancestry. Black women were the property of their White masters, and it doesn't take a Master's in history to figure out what happened there.

As far as the term "African American" goes, I suggest you read study W.E.B. Du Bois' theory of Double Consciousness as explained in The Souls of Black Folk.

Quote Originally Posted by W.E.B. DuBois
The history of the American Negro is the history of this strife, — this longing to attain self-conscious manhood, to merge his double self into a better and truer self. In this merging he wishes neither of the older selves to be lost. He does not wish to Africanize America, for America has too much to teach the world and Africa; he does not wish to bleach his Negro blood in a flood of white Americanism, for he believes that Negro blood has yet a message for the world. He simply wishes to make it possible for a man to be both a Negro and an American without being cursed and spit upon by his fellows, without losing the opportunity of self-development.