How could you have this scenario:
After the end of the First World War and the transfer of Alsace-Moselle back to France, German nationalists in the region run in elections on a platform copied from Sinn Fein's success in Ireland, abstentionism. Their aim is to win a majority of seats to the French Parliament in Alsace, and then refuse to sit in Paris, instead forming their own revolutionary 'Landtag' in Strassburg. That Landtag would then apply to join the Weimar Republic as a constituent land.
The German Nationalists win a majority of seats in Alsace, abstain from the French legislature and form their Landtag and apply to join the Weimar Republic. The French government declares the Landtag illegal and uses coercion in Alsace. Meanwhile in Germany, emotions are stirred as the people and politicians cheer their nation on in what is now referred to as the Elsasskampf. Then, in a moment that excites Germany and shocks the world, the German foreign minister smuggles his way into Alsace and gives a stirring speech in Strassburg that is recorded on radio in which he describes Germany's sympathy for the people of Alsace and that they will be most welcome as a new Land. He tells the cheering crowd that if France were to ignore its own principles of Liberté, Egalité and Fraternité, they will have the full support of Germany and that their struggle would become the struggle of many others; of the Algerian, of the South-East Asian and of the Breton against colonialism. Alsace's wish to join the Weimar Republic is accepted in Berlin while the French are furious.
They French send in the army to occupy Alsace and the Germans consider this an invasion of their territory, a guerrilla war begins with Alsacian partisan fighters given weapons by the Reichswehr. This then leads to open war between France and Germany.