The Tswana rose to domination from among a number of powerful dynasties that spread out from the western Transvaal, around AD1200–1400. During the period AD1500–1600 the Phofu dynasty in western Transvaal disintegrated with junior brothers forming breakaway, independent chiefdoms. Oral history traditions explain this as a response to drought. The archaeological record shows populations expanding into open country in small villages with cattle corrals, but by around AD1700 the settlements were often larger towns built of stone and situated on hills, reflecting the growth of hostile states, and the need for a strong defence.