UPDATE: If you are looking for an alternative way to do this achievement, check the reply from TwoSpade found at the bottom of this guide.
This achievement can be a bit rough if you do not know the Civilization VI mechanics too well. I am unsure if I am the first to unlock this but this is how I got it.
I did unlock this on Deity as it seems difficulty affects how many cities rebel.
True Start Location Earth
Turn off all victory conditions
Dramatic Ages + Secret Societies
I played as Russia and removed all players except the Cree
Keep all other settings standard
The Cree are relatively peaceful so you do not have to worry much about your military, however, they will research and culture rush you into new eras due to Deity AI boosts.
Starting off, focus on filling your golden age meter through exploration and fighting barbarians. However, try to not go over the limit, (ex. 29/25 needed for golden age). Your points do not carry over and you will actually lose those benefits in the next era.
I built about 10 cities, 4 of which were on another continent. (Not sure if this affects the game mechanic or not). The 4 cities that rebelled were on the edge of my empire and not central.
This achievement popped when I entered the Modern Era in 1490AD. This was entirely due to the Deity AI tech and culture rush. This means you will have to keep up close to the mid-end of an era tree before they get into theirs for a chance to not go into a dark age before you have 10 or more cities established. If this occurs, I suggest restarting and focusing on settlers for the first 100 turns. Do not disregard the other mechanics as loyalty factors do come into play.
- Cities with no governor rebel more often than those without.
- Do not build monuments in your cities that are on the edge of your empire. I noticed that monuments can sometimes prevent a city from rebelling due to the +1 loyalty boost.
- Avoid upgrading those cities and try to have an amenity problem. I believe this increases the chance for rebellion as the 4 cities that rebelled had that issue.
- All 4 cities must rebel at the same time entering a Dark Age. They cannot rebel throughout a Dark Age (ex. 2 rebel on entry turn and 2 rebel after). It will not count towards the achievement.
This achievement is a bit trial and error. When playing on Immortal difficulty, I only had 1 city rebel each time. Switching to Deity and it varied from 2-4. Your best bet is to work on rapid expansion while staying in a golden age for the time being.
Good luck to everyone. Hope this helps a bit in your journey.