First Question:
A lot of the prejudices that are commonplace in American society date back to the time of slavery.
Slavery was often justified as a way of helping African-descended people. The argument was that European-descended people were more civilized, culturally-advanced and technologically driven. This patronizing attitude can still be seen in interactions between people of different races in the US.
Lack of education and illiteracy also contributed to creating a stereotype of African Americans as being less intelligent than other groups and contributed to hiding the difference in opportunities between the two groups.
Second Question:
These prejudices prevail even after abolition for two main reasons. The first one is the fact that prejudices are learned through socialization. Therefore, a child that grows up with prejudiced parents is very likely to maintain those same prejudices.
The second reason is that prejudices often serve the same purpose that they served in the time of slavery, which is to hide patterns of oppression or justify difference in opportunities. It is a useful political tool and because of its convenience people can sometimes be reluctant to let them go.
