In my case I had to puppet them after I won the war. Really if the three countries needed to form Austria-Hungary stay peaceful, they will eventually reform AH given enough time after you take the AH claims focus.

During the war Czechoslovakia, Austria and Hungary automatically joined to form Austria-Hungary after their non-aligned got high enough due to the Ottoman focus Press the AustroHungarian Claim. For help spawning items using these ID codes, please see our spawn item help page. Type the cheat code or name of an item into the search box to instantly filter 218 IDs. Examples are armor include power armor and combat armor. Armor can be equipped by your character and offers defensive bonuses. I then fought the pact of Rome through France and into Italy. Find below a list of all Fallout 4 Armor IDs. So I declared on Italy and got mil access to France and UK then I order 66’d them for an easy defeat of the allies. Unfortunately Hungary and Austria joined the Pact of Rome with Italy and then declared on Yugo which brought in France which brought in the allies. Then I just used spies to boost non-aligned in Czechoslovakia, Hungary, and Austria (in that order of importance). I basically started new games until Germany deposed hitler.

I also used order 66, so if that isn’t your thing, look away. Well it would be hard to replicate since it is non-historical.

Fallout 4 hellfire power armor