By 1728 Nassau-Saarbrücken was united with Nassau-Usingen which had inherited Nassau-Ottweiler and Nassau-Idstein. In 1735 Nassau-Usingen was divided again into Nassau-Usingen and Nassau-Saarbrücken. In 1797 Nassau-Usingen finally inherited Nassau-Saarbrücken, it was (re-)unified with Nassau-Weilburg and raised to the Duchy of Nassau in 1806. The first Duke of Nassau was Frederick August of Nassau-Usingen who died in 1816. Wilhelm, Prince of Nassau-Weilburg inherits the Duchy of Nassau. But, territories of Nassau Saarbrücken was occupied by France in 1793 and was annexed as Sarre department in 1797. Finally County of Nassau-Saarbrücken was part of Prussia in 1814.