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The practice of settled agriculture in some areas of Asia and Africa was crucial to the development of early civilizations. A. Prehistorians disagree as to whether early farmers first cultivated crops along floodplains or first tried cultivating crops in less successful environments. B. Cultivation in fertile river valleys resulted in predictable harvests, which meant that farmers no longer needed to migrate constantly in search of food. C. Because crops could be cultivated more successfully where farmers were not completely dependent on rainfall, hostilities between groups arose over control of the river systems. D. The need to organize the effort to ensure the food supply and defend the land led to the formation of elite supervising groups that eventually became the first governments. E. Increasingly centralized forms of administration resulted in the emergence of social classes and in the development of cities as trade, administration, or religious centers. F. Unlike other early civilizations, those that developed in the Indus River Valley did not have any spectacular palaces or areas for exclusive use by the authorities.