The Period of Division from, A.D., 1138 – A.D., 1314, which included nearly 200 years of feudal fragmentation and which stemmed from <answer>Bolesław III's division of Poland among his sons</answer>, was the genesis of the social structure which saw the economic elevation of the great landowning feudal nobles (możni/Magnates, both ecclesiastical and lay) from the rycerstwo they originated from. The prior social structure was one of Polish tribes united into the historic Polish nation under a state ruled by the Piast dynasty, this dynasty appearing circa 850 A.D.
What stemmed the period of division?
Bolesław III's division of Poland among his sons