association under whose auspices the Congo region (coextensive with present-day Democratic Republic of the Congo) was explored and brought under the ownership of the Belgian king Leopold II and a group of European investors.

The Committee for Studies of the Upper Congo was founded by Leopold II in 1878 with financing from an international group of bankers, following the British-American explorer Henry (later Sir Henry) Morton Stanley (Stanley, Sir Henry Morton)'s exploration of the Congo River in 1876–77. Leopold hoped to open up the region along the Congo River. Between 1879 and 1882, Stanley, under the auspices of the renamed International Association of the Congo, established several trading and administrative stations along the Congo River, including Leopoldville (now Kinshasa), and negotiated treaties with local chiefs. Returning to Europe in 1882, he reported to the association that in order for the Congo basin to be profitably opened up, a railway would have to be constructed between the upper and lower Congo rivers; a charter would have to be obtained from the European powers to build the railway and to govern the land through which it would pass.

In 1884 Stanley returned from another expedition to the Congo, having signed treaties with 450 independent African chiefs who had agreed to cede the rights of sovereignty over much of the Congo basin to Leopold's association. Moreover, since many of the chiefs had been persuaded to combine their chiefdoms, the International Association of the Congo claimed the right to govern all the territories as an independent state. No other power disputed these claims, and in April 1884 the United States became the first country to recognize them. The claims were recognized almost universally at the Berlin West Africa Conference of 1884–85, at which the major European powers met to decide questions relating to the Congo basin. At that conference Leopold was recognized as the sovereign of the new state, and the state was named État Indépendant du Congo (Congo Free State). See Congo Free State.