Austria
The Treaty of Saint-Germain of 1919 (for Hungary the Treaty of Trianon of 1920) confirmed and consolidated the new order of Central Europe which to a great extent had been established in November 1918, creating new states and altering others. The German-speaking parts of Austria which had been part of Austria-Hungary were reduced to a rump state named The Republic of German-Austria (German: "Republik Deutschösterreich"). The desire for "Anschluss" (annexation of Austria to Germany) was a popular opinion shared by all social circles in both Austria and Germany. On 12 November, German-Austria was declared a republic, and named Social Democrat Karl Renner as provisional chancellor. On the same day it drafted a provisional constitution that stated that "German-Austria is a democratic republic" (Article 1) and "German-Austria is an integral part of the German reich" (Article 2). The Treaty of Saint Germain and the Treaty of Versailles explicitly forbid union between Austria and Germany. The treaties also forced German-Austria to rename itself as "Republic of Austria" which consequently led to the first Austrian Republic.
Austria–Switzerland border
The current border is a product of the creation of the Helvetic Republic in 1798. During the 19th century it was part of the western border of the Austrian Empire and later Austria-Hungary, and in the 20th century of the First Austrian Republic, the Federal State of Austria, Nazi Germany and Allied-occupied Austria, and eventually of modern Austria since its formation in 1955. 
Liechtenstein was created as an independent principality under the Peace of Pressburg (1805), although it remained nominally a member of the Confederation of the Rhine until 1866).