During the period of the mid-19th to mid-20th century, race scientists, including most physical anthropologists classified the world's populations into three, four, or five races, which, depending on the authority consulted, were further divided into various sub-races. During this period the Caucasian race, named after people of the North Caucasus (Caucasus Mountains) but extending to all Europeans, figured as one of these races, and was incorporated as a formal category of both scientific research and, in countries including the United States, social classification.