History of Austria
Austria was dominated by the House of Habsburg and House of Habsburg-Lorraine ("Haus Österreich") from 1273 to 1918. In 1808, when Emperor Francis II of Austria dissolved the Holy Roman Empire, Austria became the Austrian Empire, and was also part of the German Confederation until the Austro-Prussian War of 1866. In 1867, Austria formed a dual monarchy with Hungary: the Austro-Hungarian Empire (1867–1918). When this empire collapsed after the end of World War I in 1918, Austria was reduced to the main, mostly German-speaking areas of the empire (its current frontiers), and adopted the name The Republic of German-Austria. However the union and name were forbidden by the Allies at the Treaty of Versailles. This led to the creation of the First Austrian Republic (1918-1933).
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.