In what year did the separation of Germany and Austria as a nation-state begin?

The separation of Germany and Austria as a nation-state began in 1806, after the fall of the Roman Empire. Then the gradually emerging Kingdom of Prussia began to gradually annex the German states north of Austria. With the end of the Austro-Prussian War in the 1860s, the Austrian Empire, once the core of Germany, was driven out of Germany's circle of friends by the Kingdom of Prussia, and had to turn to the name of the Austro-Hungarian Empire. The North German Federation, with Prussia as its core, became the representative of Germany in a practical sense. Although Germany and Austria were completely separated in the 19th century, the close relationship between the two Germanic nations still makes the two countries have a certain centripetal force. In World War I, Austria-Hungary and Germany belonged to the Central Powers. In World War II, the Austrians showed little resistance to Hitler's annexation and signed the "Act on the Reunification of Austria and Germany." To this day, although there is no possibility of Germany and Austria merging, the relationship between the two countries is still very close.