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
Elite and popular opinion in Austria after 1918 largely favored some sort of union with Germany, but it was explicitly forbidden by the peace treaties. The Austro-Hungarian Empire broke up in 1918, and on 12 November that year German Austria was declared a republic. The provisional national assembly drafted a provisional constitution that stated that "German Austria is a democratic republic" (Article 1) and "German Austria is a component of the German Republic" (Article 2). Later plebiscites in the German border provinces of Tyrol and Salzburg yielded majorities of 98% and 99% in favor of a unification with the German (i.e. Weimar) Republic.