How does Chinua Achebe, through his novel Things Fall Apart, counter the imperialist stereotypes of Africa as an uncivilized continent?

In An Image of Africa, Achebe talks at length about the grotesque and inaccurate African caricatures that inhabit the margins of Western literature and exist only to justify the condescending white narrative of the "uncivilized" continent of Africa:

Heart of Darkness projects the image of Africa as "the other world," the antithesis of Europe and therefore of civilization, a place where man's vaunted intelligence and refinement are finally mocked by triumphant bestiality (1614).

Chinua Achebe's Things Fall Apart was written in part to counteract poisonous Eurocentric depictions of Africa as a "dark" continent. Indeed, by centering the novel on the traditional warrior Okonkwo and casting white settlers as an invasive force, Achebe subverts Eurocentric expectations. One interesting section that shows that the white settlers have displaced traditional Umuofian values occurs when Okonkwo and Obierika discuss a land dispute. The white settlers installed a European judicial model in Umuofia and, in doing so, have completely upset the customs of the people. When Okonkwo asks if the white man understands Umofian culture, Obierika responds in a pointed fashion,

How can he when he does not even speak our tongue? But he says that our customs are bad. . . He has put a knife on the things that held us together and we have fallen apart (176).

Here, Achebe gives readers an often marginalized perspective. White settlers believe (perhaps sincerely) that they help "uncivilized" Africans by applying their own model of justice. Achebe shows the side often disregarded or overlooked by Western literature: he shows that this "fair and balanced" approach by white judges tosses aside decades of Umuofian customs.
Perhaps the most interesting and foreboding passage of the novel comes at the very end. After spending the majority of the novel in the native perspective, Achebe shifts the narrative focus to the white District Commissioner. The novel ends as he ponders how to work Okonkwo's story into his own book:

The story of this man who had killed a messenger and hanged himself would make interesting reading. One could almost write a whole chapter on him. Perhaps not a whole chapter but a reasonable paragraph at any rate. . . He had already chosen the title of the book, after much thought: The Pacification of the Primitive Tribes of the Lower Niger (208-9).

The ironic part here, of course, is that much more than a paragraph has already been written about Okonkwo. The arrogant District Commissioner wants to appropriate only the section that he finds interesting about Okonkwo and weave this into his own Eurocentric vision of Africa. Even the working title of his book reveals that he considers the people of the region to be monolithic, a group defined by their "primitive" nature and destined to be "pacified" by white settlers.
Thus, by writing the novel from the typically overlooked perspective of a traditional tribal man in Nigeria, Achebe subverts Western ideas about the region.
I took the passage from An Image of Africa from The Norton Anthology of Theory and Criticism, 2nd ed.