The concept of civilization by the white community in Joseph Conrad's Heart of Darkness is seemingly at the core of the author's intent—to expose the reality of what transpired in the Congo in Africa.
King Leopold II of Belgium knew that Henry Morton Stanley (explorer) had discovered waterways that allowed access to areas of Africa that were still unknown to Europeans.
...heat, tropical diseases, and the huge rapids near the mouth of the Congo River on the Atlantic had long kept the Congo's interior a mystery to Europeans.
Leopold convinced Stanley to colonize the Congo for Belgium—he wanted his country to be a major colonial power, and the Congo was just what he needed. Rich with ivory (which was in great demand in Elizabethan Europe), and later from rubber, Leopold would eventually be forced to give up his "private ownership" of Belgium, but by then...
...he had made a huge profit from the territory, conservatively estimated as the equivalent of more than $1.1 billion in early twenty-first century terms.
In terms of white civilization in the Congo...
Leopold II described his motives to the rest of Europe as springing from a desire to end slavery in the Congo...
He also insisted that his desire was to bring Christianity to the inner-recesses of this mysterious land.
To curry diplomatic favor, he allowed several hundred Protestant missionaries into the Congo.
In truth, Leopold II was motivated by pure greed. When he came to the throne, his nation was a small and poor one. Exporting natural resources from the Congo changed all that. Ironically, the King never visited Africa one time during his reign. He had others run the "company" he created, who sent the profits back to him. In carrying out this work for Leopold, the white "agents" committed terrible atrocities against the natives. The idea of doing away with slavery and bringing Christianity to the natives of the Congo was completely false. The "civilized" whites were barbaric toward the natives. They brutalized them and forced them to work for the company. Some missionaries reported to friends and family at home, what they saw:
Africans whipped to death, rivers full of corpses, and piles of severed hands...
These violent actions were visited upon adults and children alike.
In the late 1800s, Joseph Conrad earned the position of a steamboat captain in the Congo. After only six months, Conrad was too sick to continue his journey and he returned home. However, he had seen enough, and his book was based upon what he had witnessed.
The main character, Marlow, arrives at the Lower Station (the first stop on his way to captaining a steamboat). There he sees men destroying the land with dynamite for no reason. He sees natives enslaved, moving like corpses or near death; others are beaten before him, or lie dead on the ground.
The white men he encounters are primarily interested in moving up within the company. They want to be like Kurtz, the most successful agent in delivering ivory from the interior—called the Inner Station.
Revulsion grows within [Marlow] over the white man's dehumanizing colonization of the Congo.
When Marlow finds Kurtz, he realizes the man has been living among the natives, is worshipped like a god and has sunk to the "depths of degradation."
The whites—simply put—took advantage of the natives: enslaved and killed them. These African people were not civilized by whites, but were brutalized by them—all for the sake of money.