“Throughout the 18th century, most Euro-American intellectuals had believed that humans were a unified species and that differences in environment accounted for both physical and cultural variance among people.
“As early as 1811, however, a North Carolina doctor named Charles Caldwell rejected that theory, proposing instead a natural hierarchy of the races. The developing pseudoscience of phrenology, which supposedly used cranial morphology to measure intelligence, bolstered Caldwell’s theory of scientific racism. Philadelphia physician Samuel Morton’s influential 1839 study ‘Crania Americana’ used phrenology to formulate an elaborate racial hierarchy — whites at the top, Indians in the middle and Africans at the bottom….
“Gone were the days when policymakers sought to integrate ‘civilized’ Indians into the republic. By the Jackson era, American expansion showed little regard for nonwhites who stood in the way.”
— From “Slavery in Indian Country: The Changing Face of Captivity in Early America” by Christina Snyder (2010)