Austrians
Historically, Austrians were regarded as ethnic Germans and viewed themselves as such. Austria was part of the Holy Roman Empire and the German Confederation until the Austro-Prussian war in 1866 which resulted in Prussia expelling Austria from the Confederation. Thus, when Germany was founded as a nation-state in 1871, Austria was not a part of it. In 1867, Austria was reformed into the Austro-Hungarian Empire. After the collapse of the Austro-Hungarian Empire in 1918 at the end of World War I, Austria was reduced to a rump state and adopted and briefly used the name the Republic of German-Austria ("Republik Deutschösterreich") in an attempt for union with the Republic of Germany, but was forbidden due to the Treaty of Saint-Germain-en-Laye (1919). The First Austrian Republic was founded in 1919. The Third Reich annexed Austria with the "Anschluss" in 1938.
Anschluss
The idea of an "Anschluss" (a united Austria and Germany that would form a "Greater Germany") began after the unification of Germany excluded Austria and the German Austrians from the Prussian-dominated German Empire in 1871. Following the end of World War I with the fall of the Austro-Hungarian Empire, in 1918, the newly formed Republic of German-Austria attempted to form a union with Germany, but the Treaty of Saint Germain (10 September 1919) and the Treaty of Versailles (28 June 1919) forbade both the union and the continued use of the name "German-Austria" ("Deutschösterreich"); and stripped Austria of some of its territories, such as the Sudetenland.