How are the issues of race and imperialism woven into "Heart of Darkness"?
Both race (or even racism) and imperialism are treated as the common attitudes of white people at the time the book takes place. This book is set on the river Thames around the turn of the 20th century. Generally speaking, the Europeans aboard the ship (as well as most other Europeans at this time) are largely ignorant of the lives of the natives they encounter traveling. Because these natives look so very different, the general attitude is that they are sub-human - closer to animals than they are to humans. This is evidenced by the repeated referrals of black people as "niggers," "cannibals," "criminals," and "savages."
Kurtz's treatise, called the "International Society for the Suppression of Savage Customs" is yet further evidence of the elitist attitude carried by white men at this time. It is one thing to merely refer to those peoples in passing as less than human - here is a man (and the characters who support his thinking) who genuinely believes they are harmful to civilized society, so he plans to educate others to fear them.
Marlow is one of the few characters whose thoughts pose an opposition to the general attitude of indifference if not blatant disrespect. He is often reflecting with sympathy on different situations in which groups of black men are seen working or enslaved. His thoughts rarely drive him to action and even his actions (like sharing the buscuit with the man on his ship) are as slight as his sympathy - but it is clear the author presents this opposing viewpoint to remind the audience of the humanity of a group of people who are viewed and mostly treated, like animals.
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