Imagine what can happen when, for many generations, a group of people are severely and strategically oppressed. Imagine what happens to their self-esteem, their initiative, their aspirations.
Think about someone you know that was in an oppressive relationship; and then think about how significantly that relationship affected them. For myself, I know that I am still trying to work out things from a relationship that only lasted four years.
Now imagine what can happen if such treatment goes on for generations.