Anschluss

The Anschluss (German for "annexation") was the unification of Austria and Nazi Germany in March 1938. Austria did not put up a fight, but instead let the Germans simply march in and take over. Pro-unification sentiment in Austria had been strong in the wake of World War I and the dissolution of Austria-Hungary, but the peace treaties expressly forbade unification of Germany and Austria. Austria did not regain its independence until 1955.