Okay kiddo, so there was a place called Austria and it used to be part of a bigger country called Austria-Hungary. But after World War I, that big country broke apart and Austria became its own independent country.
But there was a group of people in Austria who also wanted to join with another country called Germany because they spoke the same language and shared a lot of the same culture. They called themselves the "German Nationalists."
So, they held a vote and decided to form a new country called the Republic of German-Austria and join with Germany. But some other people in Austria didn't like this idea and fought against it.
In the end, the Treaty of Versailles (which is like a big agreement between different countries) said that Austria could not join with Germany. So, the Republic of German-Austria became just the Republic of Austria and remained its own independent country.