Africans are not black,” she said. “They are Igbo and Yoruba, Ewe, Akan, Ndebele. They are not black. They are just themselves. - Isabel Wilkerson

The Great Migration in particular was not a seasonal, contained, or singular event. It was a statistically measurable demographic phenomenon marked by unabated outflows of black émigrés that lasted roughly from 1915 to 1975. It peaked during the war years, swept a good portion of all the black people alive in the United States at the time into a river that carried them to all points north and west.

In the same way that black and white were applied to people who were literally neither, but rather gradations of brown and beige and ivory, the caste system sets people at poles from one another and attaches meaning to the extremes, and to the gradations in between, and then reinforces those meanings, replicates them in the roles each caste was and is assigned and permitted or required to perform.

Caste is fixed and rigid. Race is fluid and superficial, subject to periodic redefinition to meet the needs of the dominant caste in what is now the United States.