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.
Austria–Germany relations
Modern-day Austria and Germany were united until 1866: their predecessors were part of the Holy Roman Empire and the German Confederation until the unification of German states under Prussia in 1871, which excluded Austria. In 1918 after the end of World War I, Austria renamed itself the Republic of German-Austria in an attempt for union with Germany but this was forbidden by the Treaty of Saint-Germain-en-Laye (1919). In 1938, the Third Reich, led by Austrian-born Adolf Hitler, annexed Austria in the "Anschluss".