You can earn this achievement on Historical or Non-Historical but this guide assumes you are doing this on Historical

The only things you need to research are Paratroopers and the Fighter 1 model.

First thing you will need to do is delete your entire army. Sounds crazy but you wont need them

For production make sure you keep your factories producing guns for the first 70 days before swtiching to transport planes. You will need 8 of these and after that switch to fighter 1 as you should have researched that by then.

First focus you will pick is Never Another Gallipoli

Second focus is Abanond Westminster

After that I recommend picking the two focuses at the top of the Industrial Tree, but its not mandatory. Just make sure Support the Centre Party is your fifth focus, you will need to wait until you have enough autonomy before this is possible.

After that you can pick whatever focus you want but dont go down the Political Tree. I just go down the Industrial Tree for more factories.

When you have finished researching paratroopers train 8 of them. You can probably get the achievement with two but its better to be safe than sorry.

When the Facist party has reached 40% you will most likely get an event that will give you enough support to switch ideologies. Make sure you have saved enough political power for this as well as freeing yourself from Britain.

When you are free leave the Allies, join the Axis, then justify on Hungary. Move all 8 paratroopers to Germany.

When Germany has completed the Anchellus focus move your planes and paratroops to the air base in Austria. Give your paratroopers orders to drop into Budapest and Pecs.

When your justification is done declare war and execute the order. DO NOT CALL GERMANY INTO THE WAR

They should capitulate immediately and then you can annex them. If you did this right you should have won the war and annexed them before they finnished their focus which gives them cores on Transilvania.

There, achievement complete.