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One Drop Rule
The one drop rule holds that if you have one drop of Black blood in your family, you are black. This rule's rigid racial categorization was upheld by the Supreme Court of the United States in 1896 in the case of Plessey v. Ferguson. It was decided that Homer Plessey could not ride in a railroad car reserved for whites while there was a "separate but equal" facility for blacks. The court based its decision on the fact that Plessey was 1/8 black. The rule was established during slavery so that, officially, there would be a greater numbers of black slaves.Source: PBS.org
Oppression
The state of being oppressed: Kept in subservience by coercion. Oppression is closely related to hate crimes and bias.Typically, the victims of hate/bias crimes are also the victims of oppression. Those whose culture, sexual orientation, race, religion, ethnicity, age, mental or physical ability or gender is not the socially dominant one are more likely to be kept in subservient roles in the various institutions with which they come into contact: work, school, health care, etc. With this in mind however, the mere fact that, because of one's culture, one is more likely to fall victim to oppression does not imply that all minorities of race, religion, gender etc. are oppressed. Historically, however, they have endured oppression in one form or another. Source: "Oppression, Oppressed". Illustrated Oxford Dictionary- Millennium Classic Limited Edition Collection. 1998.