Complex sentence: Due to a number of attempts by Konrad of Masovia to conquer Prussia, the Culmerland to the north of Masovia became quite devastated and Konrad feared for his own land in Masovia, so he called on the pope and the emperor for yet another Crusade.
Split into simpler sentences: Due to a number of attempts by Konrad of Masovia to conquer Prussia, the Culmerland to the north of Masovia became quite devastated. In reaction Konrad called on the pope and the emperor for yet another Crusade.