The Sudetenland and Austria had never been part of the German nation. Germany itself was not created until the 1870’s. And the League of Nations had nothing to do with it. Both Austria and the Sudetenland were part of the Hapsburg possessions.
Oh for goodness sakes, for several hundred years Vienna was the de facto capital of the German nation. The Hapsburgs were the elected Emperors almost continuosly from the beginning of the 15th century until 1806.