There is also a reason people dislike blacks. You see how that works? I know Gypsies who live a completely normal life by todays standards, which is only possible to them because pretty much no one knows that they are Gypsies. They call themselves Greek, Turkish, German etc. to get accepted.
random historic event --> whites reign over blacks --> discriminating laws --> poverty and lack of education between blacks --> cultural prejudices
These prjudices lead to more discriminating laws which leads to even more poverty and lack of education and so on.