You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Szlachta

Context:
The Period of Division from, A.D., 1138 – A.D., 1314, which included nearly 200 years of feudal fragmentation and which stemmed from Bolesław III's division of Poland among his sons, 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.

Question:
What stemmed the period of division?

Bolesław III's division of Poland among his sons