Complex sentence: Due to family relationships between Aquinos and Celanos, the village entered Celanos' possessions, during the period in which the natives of Abruzzo were at the peak of their political and economic prestige.
Split into simpler sentences: Due to family relationships between Aquinos and Celanos, the village became entered into Celanos' possession. This occurred during a period in which the natives of Abruzzo were at the peak of their political and economic prestige.