When does a social difference become a social division?

Social differences divide people from one another, but they also unite very different people. The social division takes place when some social difference overlaps with other differences. For example, The difference between the Blacks and Whites becomes a social division in the US because the Blacks tend to be poor, homeless and discriminated against. In our country, Dalits tend to be poor and landless. They often face discrimination and injustice. Thus when one kind of social difference becomes more important than the other and people start feeling that they belong to different communities. Under such situation, social difference become a social division