Leopold's administration was characterized by systematic brutality and atrocities in the Congo Free State, including forced labour, torture, murder, kidnapping, and the amputation of the hands of men, women, and children when the quota of rubber was not met. In one of the first uses of the term, George Washington Williams described the practices of Leopold's administration of the Congo Free State as "crimes against humanity" in 1890.
While it has proven difficult to accurately estimate the pre-colonial population and the amount by which it changed under the Congo Free State, estimates for the Congolese population decline during Leopold's rule range from 1 million to 15 million. The causes of the decline included epidemic disease, a reduced birth rate, and violence and famine caused by the regime