In the U.S., the concept of the one-drop rule has been chiefly applied by White Americans to those of sub-Saharan black African ancestry in the 20th century, when they were trying to maintain white supremacy.

The poet Langston Hughes wrote in his 1940 memoir:
You see, unfortunately, I am not black. There are lots of different kinds of blood in our family. But here in the United States, the word 'Negro' is used to mean anyone who has any Negro blood at all in his veins. In Africa, the word is more pure. It means all Negro, therefore black. I am brown.