Complex sentence: A qualitative change took place in the 9th century, when the Polish lands were crossed again by long-distance trade routes, with Pomerania becoming a part of the Baltic trade zone, while Lesser Poland participated in exchange centered in the Danubian countries.
Split into simpler sentences: A qualitative change took place in the 9th century, when the Polish lands were crossed again by long-distance trade routes. Pomerania become a part of the Baltic trade zone, while Lesser Poland participated in trade centered in the Danubian countries.