Complex sentence: Since the Ukrainian lands were incorporated into the Great Duchy of Lithuania, while some were annexed by the Kingdom of Poland, many boyars were equated in rights with the Polish szlachta as throughout the rest of Great Duchy of Lithunia.
Split into simpler sentences: Since the Ukrainian lands were incorporated into the Great Duchy of Lithuania, while some were annexed by the Kingdom of Poland. Since then many boyars were equated in rights with the Polish szlachta as throughout the rest of Great Duchy of Lithunia.