Article 80 of the Treaty of Versailles stated: "Germany acknowledges and will respect strictly the independence of Austria, within the frontiers which may be fixed in a Treaty between that State and the Principal Allied and Associated Powers; she agrees that this independence shall be inalienable, except with the consent of the Council of the League of Nations."
This provision was included in the treaty to prevent Germany from expanding its territory and power by uniting with Austria. The Allies were concerned that a united Germany would be too powerful and would threaten the peace of Europe.
The Treaty of Versailles was signed on June 28, 1919, and went into effect on January 10, 1920. The treaty remained in effect until 1933, when Adolf Hitler came to power in Germany and began to rearm the country.