The European colonization of Africa was one of the greatest and swiftest conquests in human history. In 1870 roughly 80 percent of Africa south of the Sahara Desert was governed by indigenous kings, chiefs, and other rulers. By 1910 nearly this entire huge expanse had become European colonies or land, like South Africa, controlled by white settlers. The bloodiest single episode in Africa's colonization took place in the center of the continent in the large territory, known as the Congo.

For centuries African slave dealers had raided parts of this area, selling their captives to American and European captains who sailed Africa's west coast, and to traders who took slaves to the Arab world from the continent's east coast. But heat, tropical diseases, and the huge rapids near the mouth of the Congo River on the Atlantic had long kept the Congo's interior a mystery to Europeans. From 1874 through 1877 the British explorer and...