Marlow grows in awareness of imperialism's evil as he travels into the Belgian Congo. Notably, it is his aunt, a female, who helps him get the job. She believes Europeans are doing good by going to the Congo and bringing Christianity and civilization to the Native peoples.
Marlow is less naive than his aunt, but to some extent, he shares in her thinking until he has the shock of arriving in Africa. Once there, he realizes that Christian or civilizing influences have nothing to do with the European presence. The Native people are brutally and shockingly exploited, and the emphasis is on profit to a cruel degree. Kurtz's mad behavior has been tolerated thus far, because of the amount of profit he brings in.
Actually witnessing imperialism firsthand, Marlow is able to perceive that the system is evil to the core. He comes home shattered and changed by his knowledge, with a much more cynical view of mankind. It is particularly mankind that he condemns. At the end, when he goes to visit Kurtz's...
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