In 1918, the Sudeten region was stripped from Austria and became part of Czechoslovakia. It remained so until the Munich Conference of September 1938, when an agreement was reached that Germany would annex the Sudetenland.
Prior to the signing of the agreement at Munich, Czech troops preemptively abandoned the German-speaking regions. In the interim period between Czech and German control, the Sudeten German Party issued its own postage stamps in the areas of Asch and Rumburg.
Additionally, a single set of stamps was designed and printed for use in Sudetenland, but was never issued.