To close the circle, the etymology of the word "nigger" (sometimes written "niger" in early days) is the Spanish "negro" = "black." The earliest citation in the Oxford English dictionary dates from the late 1700s but I've seen earlier uses in republished documents in books and collections on the history of slavery.

It certainly was a widespread term of racial abuse before the Civil War. The idea that it was not pejorative before the 1900s is odd. Possibly what Kim is thinking of is that among whites before the 1900s, being pejorative about black people was rarely questioned outside of fairly limited abolitionist and reform circles before the 1920s. Or maybe she is thinking of negro/Negro?

Interestingly, the OED contains no form of the words "racist/racism" or "racialist/racialism" in either its main body or in the 1928 supplement, suggesting that the critique of racial ideologies and racially-motivated discrimination, oppression and violence had not gained its now common name in a way wide enough to reach the OED's sourcing process (which probably had upper class and conservative biases) even that late. "Raciology" as a word for the scientific study of races is in the supplement.