The Duchy of Lorraine grew up between France and the Empire. It is one of the lands where the French and the Germans collided. French was spoken in the west and Germany in the east. Sandwiched between the two, the Dukes walked a dangerous path between the two, always trying to balance one against the other.
Amongst the provisions of the Treaty of Westphalia (1648), which ended the Thirty Years War was the return of the Duchy from the French to its rightful Duke. It took the French a century before they finally absorbed it. The descendants of the Dukes of Lorraine ruled the Empire until 1918.