Complex sentence: In 1668, French missionaries Claude Dablon and Jacques Marquette founded a mission in the area, making it the third-oldest European city west of the Appalachian Mountains, and the oldest permanent settlement in contemporary Michigan state.
Split into simpler sentences: In 1668, French missionaries Claude Dablon and Jacques Marquette founded a mission in the area. The Sault is the third-oldest European city west of the Appalachian Mountains in what is now the United States, and the oldest permanent settlement in contemporary Michigan state.