I have learned in school that the Treaty of Versailles (after World War I in 1919) contained a clause that forbade unification of Germany and Austria. Presumably it is Article 80:
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.
What I am wondering is this: do we know about other peace treaties that contain/ed similar provisions (i.e. regulations against unification, not just possible annexions)? If so, which one was signed most recently?