By the mid 1800s Africa had only sparsley been touched by European influence (trading posts on the west and east coast, and the English and Boers in South Africa) But during the mid 1870s, exploration of Africa became very popular. Explorers led great treks throughout jungles, and the common european would view these explorers as celebrities. However, the first man to think of actually colonizing Africa (specifically the Congo) was King Leopold II of Belgium.

King Leopold II convinced the most well known African explorer of the time, Henry Morton Stanley, to go on a trek throughout the Congo under the flag of the International African Association which was established by Europeans in Brussels, Belgium. Stanley traveled up the main stretch of the Congo by steamboat and established trading posts along the river.

Fastforward to the Berlin Conference of 1884: Leopold's activities in the Congo were beginning to be noticed by other European nations, and thus began the popularly termed "Scramble for Africa." England, Portugal, France, and Germany all made moves for land in Africa. It was then that Otto von Bismarck called a conference to meet and discuss the colonization of Africa, and more specifically, to dicuss the International Association of the Congo which had been formed by King Leopold II.

At this conference, Henry Morton Stanley was the only person present who had ever actually been to Africa. The other diplomats present knew very little of Africa, only what they had seen from pictures and maps. Therefore, it was Stanley who told them all about his expeditions and about King Leopold's efforts in the Congo, which he described as philanthropic and altruistic. By the end of the conference, the International Association of the Congo had gained recognition, as long as free trade for all European nations was established throughout the region.

King Leopold II, after officially gaining a colony, changed the name to the Congo Free State and named himself King Sovereign. This is where the human rights violations and mutilations come in. The economy of the Congo Free State was based on rubber and ivory. In large rubber plants, Congo natives worked basically as slaves, and if they did not collect enough rubber, the hands of their loved ones would be cut off (including children).

The first critic of the Congo was American George Washington Williams. Upon visiting the Congo he was horrified by the living conditions, the slavery, and the mass mutilation. He wrote and published a letter to King Leopold II of Belgium (which can be found here http://www.blackpast.org/george-washington-williams-open-letter-king-leopold-congo-1890), which openly condemned Leopold and his Congo operations. Prior to William's letter, most people were oblivious to what was going on in the Congo. They still believed that the Congo was being westernized and christianized for the better, and this is why the letter came as such a shock. Other prominent people followed William's footsteps and openly criticized King Leopold's Congo. Mark Twain published King Leopold's Soliloquy and Sir Arthur Conan Doyle published The Crime of the Congo. Heart of Darkness came next, published in 1899.

Sources: King Leopold's Ghost by Adam Hochschild, George Washington Williams's Open Letter to King Leopold on the Congo 1890, The Treaty of Berlin 1885