I made this achievement with 1.0.1 version of HoI 4.
Historical up.

I will write how i made the achievement, to give some ideas. This is just one way to get the achievement.

Goal of this achievement is : Must control the state of Svealand as a communist Denmark.
As soon as we occupy the state of Svealand with our troops, we receive the achievement. No matter who is winning the war.

General plan : My thought was that i would never manage to make a naval invasion on Sweden with Denmark (maybe i am totally wrong), so i chose to conquer Norway first before attacking Sweden.

First difficulty is that Denmark has no steel, and has a very poor industry.
Against the poor manpower of Denmark, i ended the game with a high level of conscript.

Political choices :
My first choice as political idea was the "political effort". When it was completed, i used the communist advisor.
After that i took all the Industry political ideas before anything else.
And only then, i began with Infantry.

The researches :
I had 2 priorities : land doctrines (i chose superior firepower) and industry researches.
I developped small weapons, support and artillery ; no boats nor planes.

The constructions :
I built only military factories, and one fort near copenhagen, but i guess that this fort was more a psychological need than a real usefulness. :)

The productions :
I only produced 3 things : small weapons, support and artillery. And nothing else.

The division model :
I first wanted the number of divisions, so the only change i made to the model was to add the recon support before attacking Norway. During the Norway war, i added some batallions.
When i completed the achievement, i had 18 diviions..

My behaviour concerning the "no steel" fact :
When playing HoI4 i usually wait the moment i need 8 ressources to buy them. This time i made the opposite. I bought 8 steel to Ussr before i was in need. When the 8 were consumed i bought a new pack. I wanted my industry to work at full speed.

The beginning is very slow concerning the troops.

When i became communist, i launched my war demands on norway.
When i declared war on Norway, i had 10 divisions.

The Norway war was easy. They had a poor army.
When i took the south part of Norway, i launched my war demands on Sweden.
Half way to the new main city of Norway, they surrendered. I took all the states.

I used my xp to increase the number of battallions of my division model.

I put my army at the right of Oslo, at the Sweden border. I had 18 divisions at that moment.

When i declared war on Sweden, France had put a guarantee on them.
In declaring war to Sweden, i entered the world war. So i joined the Kommintern. Just in case, i didn't want to be focused by the allies.

For me, at that moment, there was only one thing left to do : rush the Svealand state.
There was only a small resistance on the way to Stockholm. Sweden took the north of Norway. This was a good point as these swedish troops were not defending Stockholm.
I made some micro management here, especially to have some divisions keeping the provinces of Svealand i took, while the rest of my army kept running towards Stockholm.

When i occupied the last province of the Svealand state, i received the achievement.
I was still in war with Sweden ... and the rest of the world. :)



Thank you, and have fun :)