Joseph Conrad, 1899 (carrying into 20th-c canon). Marlow's Congo expedition — colonialism's foundational indictment.
From Wikipedia
Heart of Darkness is an 1899 novella by Polish-British novelist Joseph Conrad, in which sailor Charles Marlow tells the story of his assignment as steamer captain for a Belgian company in the African interior. The novel is widely regarded as a critique of European colonialism in Africa, whilst also examining the themes of power dynamics and morality.