If you want to successfully oppress and exploit all the people you must make sure that you visibly oppress an identifiable minority far more than the rest of the population. That way the majority of the population will assume that they themselves are not being exploited and oppressed and many of them will actually feel guilty if they complain about their own lot. So much energy will be put into protesting against the oppression of the minority that nobody has enough energy left to protest about the wrongs being committed against everybody. Of course, everybody getting together and fighting the oppressors takes no more energy than everybody getting together to sort out the minority's problems. But that never seems to occur to anyone.