How did stereotypes about African-Americans evolve throughout history?

That is a big assignment requiring a lot of study and a lot of personal interpretation of what you find.

First, stop calling black people "African-Americans". Africa is not a country, not all Africans are black, and some black people did not come from Africa.You are talking about ex-slaves, and the historically correct term for them was negroes. According to the US constitution, a slave was equal to three fifths of a human. (Article 1 Section 2)

During slavery there were strong efforts to break the spirits of all male slaves. One of the more blatant methods was to beat the man in sight of his woman, and then deal with the woman in a businesslike manner. That led to a matriarchal society and spineless men. The effects of that program continue to the present day.

Nobody has ever determined a clear reason for the civil war, but the aftermath was clearly intended to punish the south. Southern lawmakers tried to ease the pain on their constituents by passing laws favoring whites over negroes. (The Jim Crow era.) Those laws continued until the mid-60s.

Walt Disney was a major contributor to stereotypes, and so were other cartoonists of the 1940s. The Disney movie "Song Of The South" all by itself created the stereotype that negroes danced a lot and sang a lot of songs of a unique nature. The Irish term "jig", a style of dancing, came to mean a negro because of that one movie. You can go to thepiratebay.org (but not on a school computer) and search for "banned cartoons" to see what was common in movie entertainment in the 1940s. I promise you will be astounded.