In the Descent of Man Darwin "discussed perishing barbarians, the elimination of savages and the inevitable prospering of civilized nations," as reviewed in the June 2005 American Spectator.
Looks like a good book. I'm going to read it.
Lots of people believed in eugenics, not just Darwin. Take US Supreme Court Justice Oliver Wendell Holmes, Jr. in Buck v. Bell (1927) for instance. "It is better for all the world, if instead of waiting to execute degenerate offspring for crime, or to let them starve for their imbecility, society can prevent those who are manifestly unfit from continuing their kind…Three generations of imbeciles are enough."