Complex sentence: The history of Poland during the Piast dynasty is the first major stage in the history of Poland from the 10th to the 14th century when Poland was established as a state and a nation during the medieval period of European history.
Split into simpler sentences: The history of Poland during the Piast dynasty is the first major stage in the history of Poland. The period lasted from the 10th to the 14th century when Poland was established as a state and a nation during the medieval period of European history.