Do they? There is indeed a black history that goes back much farther than 400 years, but it is limited by two factors: they were not a literate people or rather, they did not record their history in ways that are easily retrievable today, and secondly, the population of Africa was nowhere near the population of the rest of the world, not was it even proportionaly equal to the persons per square mile populations of the rest of the world, which reduced the amount of historical record that could be expected.