Children of Afrika Series with Andre Harris,Chris Clarkson,Chief. Africa is the world's second largest and second most-populous continent. At about 30.3 million km² including adjacent islands, it covers 6% of Earth's total surface area and 20% of its land area. With 1.2 billion people as of 2016, it accounts for about 16% of the world's human population. Slavery in the United States was the legal institution of human chattel enslavement, primarily of Africans and African Americans, that existed in the United States of America in the 18th and 19th centuries.