The area north of the Congo River came under French sovereignty in 1880 as a result of Pierre de Brazza's treaty with Makoko of the Bateke. This Congo Colony became known first as French Congo, then as Middle Congo in 1903. In 1908, France organized French Equatorial Africa (AEF), comprising Middle Congo, Gabon, Chad, and Oubangui-Chari (the modern Central African Republic). The French designated Brazzaville as the federal capital. Economic development during the first 50 years of colonial rule in Congo centered on natural-resource extraction. The methods were often brutal: construction of the Congo–Ocean Railroad following World War I has been estimated to have cost at least 14,000 lives.

When did the French take control of the region to the north of the Congo River?