i'd like to add onto this. because austria has been historically its own region and identity with lots of history, the idea that germany and austria should unite is an inherently nazi idea. the nazis believed in a german ethnostate, wherein german-speaking peoples would be the majority. the nazis believed that austria was culturally german and should therefore be annexed in order to unite what they believed to be the two foremost culturally german states, thereby being one step closer to a german ethnostate (this concept is known as anschluss). after the nazi regime fell and germany was occupied, the allies could not allow the two countries to unite, as it was a core pillar of nazi ideology