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
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.