Complex sentence: The local branch of Silesian Piasts has died out by 15th century; the Duchy, under various rulers, remained in Bohemian sphere of influence until Silesian Wars of 18th century, when it was conquered by Prussia.
Split into simpler sentences: The local branch of Silesian Piasts has died out by 15th century. The Duchy, under various rulers, remained in Bohemian sphere of influence until Silesian Wars of 18th century, when it was conquered by Prussia.