I’ve encountered this several times now in my research: during the late eighteenth/early nineteenth century, “anti-racism” was briefly ascendant in social science in Britain and the United States, and it later lost influence during the antebellum era, waxed again during Reconstruction, and waned during the Jim Crow era.
Stephen Drescher brings this up in reference to the failed utopian experiment in free labor in Sierra Leone:
“Thomas Winterbottom, a physician, was to study tropical medicine. He became the dominant ethnographer of West Africa and contributed to the antiracist scientific tradition that dominated British racial science during the first third of the nineteenth century.”
In France, anti-racism was ascendant under the Jacobins who abolished slavery in all the colonies of the French Empire and made blacks into citizens with equal rights.
Later under the Consulate, Napoleon restored slavery, banned the Black Undertow from the soil of the Republic, banned miscegenation, and arrested the black members of the French parliament.
I want to say that blacks became French citizens after slavery was abolished in the Second Republic following the 1848 Revolution and later gained voting rights in France in 1870 during the Third Republic.
I know for certain that the story rise and fall of racialism in the West is far more complex than most White Nationalists commonly assume.
Update: Drescher cites Philip Curtin’s The Image of Africa: British Ideas and Action, 1780-1850. Google Books has a preview. This should definitely be worth reading.