Origin of the term White Supremacy?

Question

What is the origin of the term "white supremacy"?

Online Etymology Dictionary gives this as the origin of the term:

White supremacy attested from 1868, American English [John H. Van Evrie, M.D., "White Supremacy and Negro Subordination," New York, 1868]....

Yet OED records earlier attestation:

The belief or theory that white people are superior to other peoples, and should therefore have greater power, authority, or status. Also: a social system based on or perpetuating the political, economic, and cultural dominance of white people.
1824 T. S. Winn Emancipation 57 It may be too late by any means, however wisely and honestly attempted, to reduce them to order and obedience under White supremacy, or even among themselves.
1839 H. Bevan Thirty Years India II. xviii. 299 The security of our empire in the East would be greatly strengthened if..our functionaries would abandon, or at least conceal, those notions of White supremacy, which are frequently absurd, and always offensive.

The disparity between those two sources suggests the story presented may be incomplete, and neither source delves into preceding terminology that might have helped to chart the course of the development of the term.

Who was the first person to use the term?

How has the meaning changed or developed?

In which historical periods has the term been used most often?

Answer 1

OED places the first attested use in 1824:

1824 T. S. Winn Emancipation 57 It may be too late by any means, however wisely and honestly attempted, to reduce them to order and obedience under White supremacy, or even among themselves.

This early use, of which a larger passage can be accessed on google books here, does not seem to treat the concept of "White supremacy" as a concept to be abhorred. Perusing newspaper articles from the 19th century indicates that the term "white supremacy" was often used without a negative connotation in the 19th century, especially in southern states. Describing "white supremacy as a societal problem increased over time, especially as the term gained stronger footing in the 20th century.

Google Ngram indicates that popular use of the term took off in the 20th century.

Throughout the 20th century, the meaning of the term has remained mostly static. It still refers to, as OED puts it,

The belief or theory that white people are superior to other peoples, and should therefore have greater power, authority, or status. Also: a social system based on or perpetuating the political, economic, and cultural dominance of white people.

As movements for racial equality gained ground in the U.S. throughout that century, the use of the term was more likely to be disparaging or treated as a problem than it was during the 19th century, but the meaning of the phrase is understood the same way. Whether or not the movement or theory itself is viewed as loathsome depends on the perspective of the person using the term and their attitudes about race.