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Blood quantum is a concept that was created to determine which race a person is on the basis of ancestry. It is often described as a colonial construct that was made to destroy indigenous communities.

The blood quantum concept was invented in the Thirteen Colonies to categorize African-Americans and Native Americans by ancestry in order to segregate them from white people.

The practice of blood quantum was also used to justify the notion that certain people who are "full-bloods" are racially incapable of managing their own affairs, while those with white ancestry are worthy of being in white society. In other cases, blood quantum was used to segregate indigenous peoples with "full-blood" descent and remove people with partial white ancestry in an attempt to assimilate them in white society, such as the case with the Stolen Generations in Australia. The practice was also used by some organizations such as the Bureau of Indian Affairs to exclude certain races from being enrolled in a federally recognized Native American tribe if they lack any native ancestry.

The concept of blood quantum has been defined by some as an act of racism and genocide, since it was established to destroy racial groups based on race.