Simplify the following text for a Grade 8 native English-speaking person.
Original: Poland during the Piast dynasty is the period of the formation and establishment of Poland as a state and a nation . The historically recorded Polish state begins with the rule of Mieszko I of the Piast dynasty in the second half of the 10th century .
Simplified: Poland began to form into a country around the middle of the 10th century in the Piast dynasty .