Complex sentence: He was Duke of Środa Śląska ("Neumarkt") in Silesia from 1277 and during his reign the second Mongol raid against Poland, led by Nogai Khan occurred.
Split into simpler sentences: He was Duke of Środa Śląska in Silesia from 1277 onward. During his reign the second Mongol raid against Poland, led by Nogai Khan occurred.