The phrase "Your new-caught sullen peoples, / Half devil and half child" is an example of Scientific racism, a belief that Europeans used to justify imperialism.
That line was written by Rudyard Kipling in "The White Man's Burden," and this part show ethnocentrism, which means judging other cultures.
European nations considered themselves to be better than other races. Not only better but more powerful, which gave them the right to conquer other nations considered "weaker," as was the case with territories in South America of Africa. That is why the conquered new lands and exploited them, knowing that they hand a lot of raw materials and natural resources.
