The Sudetenland was a mountainous region of the Austro-Hungarian Empire, located on the northwestern border with Germany. From ancient times, it had been inhabited by German-speaking people. Around 6th century BC, it was first settled by a Celtic ethnic group and, by the 1st century BC, it had been conquered by the Marcomanni, a Germanic tribe that settled there permanently. In the Middle Ages, the Sudetenland became part of the Duchy of Bohemia and the Holy Roman Empire of the German Nation. In the late 19th and beginning of the 20th century, it was a small portion of Austria-Hungary. However, right after World War I, the Sudetenland became a western portion of Czechoslovakia, which was created in 1919 by the Treaty of Versailles. In September 1938, it was annexed to Germany by Adolf Hitler.
Map of the Sudetenland