uhm.. Bolesław Chrobry , first king of Piast dynasty was crowned in 1025ad...
also, during Gniezno Meeting ( 1000ad ) HRE emperor Otton III gave him royal insignias and secular coronation, proclaiming Bolesław friend of Empire and brother of Emperor. Unfortunatly Otton III died 2 years later and next emperor wasnt so friendly which resulted in kinda bloody relations

, so Bolesław had to wait till 1025ad for Pope to send him royal crown becoming first official king of Poland. Period you are refering to is after death of king Bolesław Krzywousty in 1138ad when kingdom was divided between his sons, each ruling his own province. Also, during that time, ( 1228ad ) one of the princes , Konrad Mazowiecki invited Teutonic Order to help him fight pagans in Prussia . And finaly, after many years of bitter fighting for royal crown Poland was united again in 1320 when Władyslaw Łokietek was crowned as king of Poland.