Why does America ignored Sub Saharan African civilizations?

I always hear negative stuff about Africa mainly in the Sub Sahara.I hear that all blacks did were having their tribal wars living in huts hunting down gazelle. As an African American myself I know thats not true. I've studied African history and culture, reading about great civilizations that once thrived there such as the Kingdom of Benin and the Fon city of Dahomey that developed a female army known as the Ahosi. Also the Nok Civilization who brought iron melting to the Sub Sahara. I hear it ignored because negroes didn't have a form of writing. And civilizations started when writing began. Does this make them a civilization at all? Or, did civilization really started with art in scuplture? Even so why ignore it?