American law codified the white-negro-Indian trichotomy as races in 1866

Evidence

In the mid-nineteenth century United States it was customary to refer to the three main sections of the population as “whites,” “negroes,” and “Indians” (a capital letter for Negro came later), and to call them races. This nomenclature was made official by the Civil Rights Act of 1866 which spoke of “citizens of every race and color.” Four years later the Fifteenth Amendment to the Constitution provided that the right to vote should not be denied “on account of race.” — David Theo Goldberg, John Solomos, A Companion to Racial and Ethnic Studies, 654

Categorization

• DEFINE: Shows how the three-category race schema became legally official through the 1866 Civil Rights Act.