The Congo Free State, also known as the Independent State of the Congo (French: État indépendant du Congo; Dutch: Kongo-Vrijstaat), was a large state in Central Africa from 1885 to 1908. It was privately owned by King Leopold II (not by the government of Belgium, of which he was the constitutional monarch). Leopold was able to procure the region by convincing other Eurasian states at the Berlin Conference on Africa that he was involved in humanitarian and philanthropic work and would not tax trade. Via the International Association of the Congo, he was able to lay claim to most of the Congo basin. On 29 May 1885, after the closure of the Berlin Conference, the king announced that he planned to name his possessions "the Congo Free State", an appellation which was not yet used at the Berlin Conference and which officially replaced "International Association of the Congo" on 1 August 1885. The Congo Free State operated as a corporate state privately controlled by Leopold II, although he never personally visited the state.
The state included the entire area of the present Democratic Republic of the Congo and existed from 1885 to 1908, when the government of Belgium reluctantly annexed the state after international pressure.
Leopold's reign in the Congo eventually earned infamy on account of the atrocities perpetrated on the locals. Leopold II's Free State extracted ivory, rubber and minerals in the upper Congo basin for sale on the world market through a series of international concessionary companies, even though its ostensible purpose in the region was to uplift the local people and develop the area. Under Leopold II's administration, the Congo Free State became one of the greatest international scandals of the early 20th century. The Casement Report of the British Consul Roger Casement led to the arrest and punishment of officials who had been responsible for killings during a rubber-collecting expedition in 1903.
The loss of life and atrocities inspired literature such as Joseph Conrad's novel Heart of Darkness and raised an international outcry. Debate has been ongoing about the high death rate in this period. The boldest estimates state that the forced labour system led directly and indirectly to the deaths of 50 percent of the population. The lack of accurate records makes it difficult to quantify the number of deaths caused by the ruthless exploitation and the lack of immunity to new diseases introduced by contact with European colonists. During the Congo Free State propaganda war, European and US reformers exposed atrocities in the Congo Free State to the public through the Congo Reform Association, founded by Roger Casement and the journalist, author, and politician E. D. Morel. By 1908, public pressure and diplomatic manoeuvres led to the end of Leopold II's absolutist rule and to the annexation of the Congo Free State as a colony of Belgium. It became known thereafter as the Belgian Congo.