Answer
The Sudetenland, where Henlein lived, had become a part of Czechoslovakia after World War I. Czechoslovakia was created in 1918 as a new country in the aftermath of the collapse of the Austro-Hungarian Empire. The Sudetenland was a region of Czechoslovakia that was inhabited by a large German population. Henlein was a German-speaking Sudeten German who was a member of the Sudeten German Party.