Which rule was based upon an individual African American's family history?

The "Rule of One-Drop" was based on the concept of tracing an individual's racial identity through their ancestry, particularly in the context of African American heritage. This rule posited that if a person had even a single ancestor of African descent, they were considered Black, regardless of their appearance or how they identified. This social construct was used to enforce racial segregation and discrimination, significantly impacting family histories and identities within the African American community.