Last year, I saw an interview with Walter McDougall on Booknotes about his book, Promised Land, Crusader State : The American Encounter With the World Since 1776. His thesis is that America is torn between two competing & diametrically opposed impulses. On the one hand, we want to be a Shining City on a Hill, uncontaminated by contact with the outside world. But on the other hand we long to bring freedom, democracy, etc. to other nations.
The reasons for this dichotomy have never been presented with more power than they are in Heart of Darkness. It is the story of how the Imperial impulse--bringing civilization to the savages--corrupts the bringers.
Marlow, a steam boat pilot, sets off upriver in Africa to find Kurtz, an ivory trader who has gone native. Along the way, he finds a pamphlet that Kurtz wrote about the civilizing mission of the White man, which ends with the postscript "Exterminate all the brutes!" When, Marlow finds the mortally ill Kurtz, in a camp surrounded by pikes with human heads mounted on them, he has stopped trading for ivory & has instead taken to raiding villages & taking it by brute force. He has abandoned civilized norms and has adopted the methods of the natives.
Kurtz final words to Marlow are "The horror. The horror." When Marlow returns to Europe he meets Kurtz fiance & when she begs to know if Kurtz spoke of her, Marlow tells her that he died with her name on his lips. It is not just the savagery of the natives that is corrupting, it is the very notion of a civilizing mission. Conrad is wrong, of course, but it's a great book.