Similar to the word nigger - a racially defining term that is inherently racist. However, unlike the term nigger, cracker is not remotely taboo to use against Caucasians by Americans of African descent as nigger is when used by Caucasians to identify Americans of African descent. See double standard, reverse racism.
The mistaken belief among many Americans of African descent that culture as we know it arose in Sub-Saharan Africa. Those taken in by such foolishness believe that they are the heirs of the Egyptian race, forgetting, of course, that this distinction actually belongs to today's Egyptians, and ignoring the fact that there is absolutely no evidence for such a preposterous claim. This cult-like mentality is often spouted by the likes of Louis Farrakhan, the NAACP, the Nation of Islam and others who have never been to Africa and who would never be caught dead there.