1930 High school best-selling textbook
by Elliot Morrison and Henry Steele Commager

Sambo, whose wrongs moved the abolitionists to warth and tears . . . suffered less than any other class in the South from its "peculiar institution." . . . The majority of slaves were . . . apparently happy. . . . There was much to be said for slavery as a transitional status between barbarism and civilization. The negro learned his master's language, and accepted in some degree his moral and religious standards. In return he contributed much besides his labor—music and humor for instance—to American civilization.