Hello, this achievement will get you the "Party like it's 1520 achievement" where you need to be a communist Denmark and own Stockholm, enjoy!
So I did this achievement in a much different way from others, I made my own strategy and basically got the achievement in one try, in like only one hour, so here's how I did it!

Step 1. Play as Denmark and hire a FASCIST demagogue, it may seem confusing now but it comes together later..

Step 2. Join the Axis and justify on Sweden.

Step 3. After the Justification is finished, declare war and call Germany into it.

Step 4. Germany will do all the work and basically conquer Sweden.

Step 5. Hire a COMMUNIST revolutionary.

Step 6. While still at war with Sweden, ask Germany for the state that Stockholm is in, by clicking on Stockholm.

Step 7. Turn communist and get the achievement.

Simple, right? This is what I did and I think it's so easy, just people haven't found the loophole yet, so time to share it, enjoy the achievement, and thanks for reading!