Assassination
On 24 November 1227, during a diet of the Polish Piast dukes at Gąsawa, he was assassinated, probably on orders from Duke Swietopelk II of Pomerelia. This was the result of Leszek having attempted to force the Pomeranian duke to submit to his authority. Swietopelk upon Leszek's death declared himself independent from Polish vassalship.
His son Bolesław V was still a minor upon his father's death and the rule over Poland remained contested between Leszek's brother Konrad and his Greater Polish cousin Władysław III, until in 1232 Duke Henry I the Bearded of Silesia finally prevailed.
Read more about this topic: Leszek I The White