Why is the Rhine valley provinces of Alsace and Lorraine been a source of conflict between France and Germany?

The Rhine valley provinces of Alsace and Lorraine have been a source of conflict between France and Germany primarily due to their strategic location and rich resources, making them economically significant. Historically, the regions have switched hands multiple times, particularly after the Franco-Prussian War in 1871 and World War I. This territorial tug-of-war has fueled nationalistic sentiments and cultural identities, as both countries claim historical and emotional ties to the area. The disputes over Alsace and Lorraine underscore broader themes of national identity and territorial sovereignty in European history.