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Vorarlberg following a referendum held there in 1919, in which 81% of the people of Vorarlberg voted to join Switzerland; but Vorarlberg was instead incorporated into the First Austrian Republic.
Suppose however it joned Switzerland.
I'm not sure why it didn't, the language there is Swiss German, its comparable in size to the existing Swiss cantons.
Doing so would have made the principality of Liechtenstein an enclave within Switzerland, but its partially controlled by them anyway.
So suppose it is, in 1920 it becomes a Swiss Canton.
Would Hitler demand its return? Or would it be like the area Denmark took, the Germans never took that back even while occupying Denmark.