American history describes the political entity that began with the arrival of the first permanent European settlers in 1620. Black history describes the span of time that began at the dawn of humanity. As of this writing, we know that the first human was a Black woman. Thus, Black history stretches from her birth until the present day.
We clear up much of the confusion in our article titled Black History Is World History and World History Is Black History here https://www.panafricanalliance.com/black-history-is-world-history-and-world-history-is-black-history/