Chinua Achebe in an early essay on Conrad's novel The Heart of Darkness was one of the first ones to see Conrad's literary project as a colonial form. Afterwards, Conrad has been subject to much more complex and subtler postcolonial problematization.
Achebe's basic point is that Marlowe's and Dr. Kurtz's jouney into the interiors of Black Africa is an attestation of the colonial project of 'civilizing' the barbaric tribes down there. The famous 'horror' of Dr. Kurtz is to him, the horror of the savages. The Conradian stress on the savagery of the Blacks is a racist position, in Achebe's opinion and this is what justifies the colonial mission of enlightenment. The title-expression "heart of darkness" takes for granted, the equation between racial blackness and epistemic void, making animals out of the Blacks, dehumanizing them in the process. The tragic death of Kurtz is a way of highlighting the cruelty of the Blacks and the great, noble and self-sacrifical colonial project of the 'White Man's Burden'.