how is power abused in joseph conrad' s Heart of Darkness

Much of your question has to do with early colonialism in Africa. European powers all wanted a piece of the continent to exploit. In Heart of Darkness we see some of the worst examples of abuse. To the companies that exploited Africa, it was a place to be plundered and mined. It was a new world to be conquered. Ivory and gold were popular commodities. The indigenous people were savages who could be used for slave work. The companies liked Africa because her treasures were free for the taking and her people were expendable. One of the more disturbing examples of this was when Marlow stumbles onto what he calls "the grove of death". Here workers brought from along the coast were cast aside when they were found too sick to work,

"Brought from all the recesses of the coast in all the legality of time contracts, lost in uncongenial surroundings, fed on unfamiliar food, they sickened, became inefficient, and were then allowed to crawl away and rest. These moribund shapes were free as air--and nearly as thin."

The racism, abuse and dehumanisation are all implicit in this quote.