One-drop rule: Legislation and practice
Both before and after the American Civil War, many people of mixed ancestry who "looked white" and were of mostly white ancestry were legally absorbed into the white majority. State laws established differing standards. For instance, an 1822 Virginia law stated that to be defined as mulatto (that is, multi-racial), a person had to have at least one-quarter (equivalent to one grandparent) African ancestry. Social acceptance and identity were historically the keys to racial identity. Virginia's one-fourth standard remained in place until 1910, when the standard was changed to one sixteenth. In 1924, under the Racial Integrity Act, even the one sixteenth standard was abandoned in favor of a more stringent standard. The act defined a person as legally "colored" (black) for classification and legal purposes if the individual had any African ancestry....
Pursuant to Reconstruction later in the 19th century, southern states acted to impose racial segregation by law and restrict the liberties of blacks, specifically passing laws to exclude them from politics and voting. From 1890 to 1908, all of the former Confederate states passed such laws, and most preserved disfranchisement until after passage of federal civil rights laws in the 1960s. At the South Carolina constitutional convention in 1895, an anti-miscegenation law and changes that would disfranchise blacks were proposed. Delegates debated a proposal for a one-drop rule to include in these laws....
In 1865, Florida passed an act that both outlawed miscegenation and defined the amount of Black ancestry needed to be legally defined as a "person of color". The act stated that "every person who shall have one-eighth or more of negro blood shall be deemed and held to be a person of color." (This was the equivalent of one great-grandparent.) Additionally, the act outlawed fornication, as well as the intermarrying of white females with men of color....
Jim Crow laws reached their greatest influence during the decades from 1910 to 1930. Among them were hypodescent laws, defining as black anyone with any black ancestry, or with a very small portion of black ancestry. Tennessee adopted such a "one-drop" statute in 1910, and Louisiana soon followed. Then Texas and Arkansas in 1911, Mississippi in 1917, North Carolina in 1923, Virginia in 1924, Alabama and Georgia in 1927, and Oklahoma in 1931. During this same period, Florida, Indiana, Kentucky, Maryland, Missouri, Nebraska, North Dakota, and Utah retained their old "blood fraction" statutes de jure, but amended these fractions (one-sixteenth, one-thirty-second) to be equivalent to one-drop de facto.
Before 1930, individuals of visible mixed European and African ancestry were usually classed as mulatto, or sometimes as black and sometimes as white, depending on appearance. Previously, most states had limited trying to define ancestry before "the fourth degree" (great-great-grandparents). But, in 1930, due to lobbying by southern legislators, the Census Bureau stopped using the classification of mulatto. Documentation of the long social recognition of mixed-race people was lost, and they were classified only as black or white....