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In their attempt to ensure white supremacy decades after emancipation, in the early 20th century, most southern states created laws based on the one-drop rule, defining as black, persons with any known African ancestry. This was a stricter interpretation than what had prevailed in the 19th century; it ignored the many mixed families in the state and went against commonly accepted social rules of judging a person by appearance and association. Some courts called it "the traceable amount rule." Anthropologists called it an example of a hypodescent rule, meaning that racially mixed persons were assigned the status of the socially subordinate group.

What was the rule in the 1800s called?
the traceable amount rule