Historically, "a civilization" has often been understood as a larger and "more advanced" culture, in implied contrast to smaller, supposedly primitive cultures. In this broad sense, a civilization contrasts with non-centralized tribal societies, including the cultures of nomadic pastoralists, Neolithic societies or hunter-gatherers; however, sometimes it also contrasts with the cultures found within civilizations themselves. Civilizations are organized densely-populated settlements divided into hierarchical social classes with a ruling elite and subordinate urban and rural populations, which engage in intensive agriculture, mining, small-scale manufacture and trade. Civilization concentrates power, extending human control over the rest of nature, including over other human beings.