Complex sentence: Dukagjini then tried to ally himself with Venice by accepting Venetian suzerainty and granting them control of Dagnum, but as Venice didn't want to provoke Ottoman hostility refused any involvement and returned the fort to Ottoman control by 1435.
Split into simpler sentences: Dukagjini then tried to ally himself with Venice by accepting Venetian suzerainty and granting them control of Dagnum. However, as Venice did not want to provoke Ottoman hostility, it refused any involvement and returned the fort to Ottoman control by 1435.