Short answers, pulled from the story.
King Leopold II of Belgium announced the creation of the Congo Free State on the 29th of May 1885. This declaration occurred just days after the conclusion of the Berlin Conference on Africa which gathered fourteen European nations to negotiate the partition of the African continent.
Irish diplomat Roger Casement identified four main causes for population loss including indiscriminate war, starvation, reduced birth rates, and disease such as sleeping sickness. Estimates regarding total fatalities vary considerably among historians with some figures ranging from five million to ten million deaths while current research suggests one point two to one point five million fewer people existed in 1924 compared to 1885 levels.
The Force Publique served as a private army composed of white European officers and black soldiers who enforced rubber quotas through systematic terror using modern weapons and chicotte bullwhips made from hippopotamus hide. Soldiers routinely took hostages slaughtered families of rebels and raped Congolese people across vast territories while requiring one hand for every bullet spent by subordinates to prevent ammunition waste.
Edmund Dene Morel founded the Congo Reform Association shortly after receiving findings from British Consul Roger Casement about alleged violations of the Berlin Agreement. The organization spread branches as far as the United States to coordinate international opposition against the commercial trust oriented entirely toward profit that functioned as the government.
The parliament of Belgium annexed the Congo Free State on the 15th of November 1908 taking over its administration as the colony of the Belgian Congo. This decision followed two years of debate and new elections held specifically on the issue which were driven by international pressure making Belgium the obvious European candidate to assume responsibility for ruling the territory.