1. The player must choose a nation at the start of the game and only act as the one he chose.

2. In case the nation is destroyed, the player may still hope for a rebellion and keep playing if it occurs and the nation reforms.

3. In case the nation is unified, the player may continue playing as the nation he unified with (optional hard mode: you can rule a game over if you join another nation instead of the other nation joining yours)

4. In order to provide a fair challenge, the player is limited to certain actions:
Wars -> Attack
Alliances -> Leave, Donate
Internal Commands -> Rename, Recolor

5. No wars to death, but the player may attack in quick succession

6. No Core making, it must happen naturally with gold from your nation AI

7. The player cannot disable his nation AI (since he will rely on it for some interactions)

8. The player cannot check other nations for their Gold, Combat Efficiency or Revolt Chance

9. The player must hide Gold in the Display Options, but keep Icons (optional hard mode: Icons are hidden too)

If there's no other nation left, the player wins
If the chosen nation is wiped off the map and no cities remain for a revolt, the player lose.

Start Wars - ON
Winner Takes It All - OFF

Join Alliances - ON
Leave Alliances - ON
Max Alliance Size - 5% of starting nations (recommended, but not a strict rule)

Core Purchases - ON
Donations - ON
Unifications - ON

Revolts - ON
New Nations - OFF

Combat Efficiency - PROGRESSIVE (IMPORTANT as otherwise it's too random)

Allow Razing - OFF
Remove Exclaves - OFF

You cannot force Peace, Annex, Ally, Revolt or Make Core for obvious reasons (you must live with the consequences of your actions)
However, those may occur naturally with your Nation AI (hence why you must not disable it)

You also can't prevent your nation to send donations to allies, so think twice if it's better to stay or leave an alliance.

It's best to attack nations when your Combat Efficiency is high and your neighbor's is low, but wars may keep going for a long time and you cannot force peace, so there's always a possibility that they mount a counter attack and you end up losing terrain.

Remember, you cannot check other nations, so you know your own efficiency, but you may never be sure how your neighbors fare except with the "strong" or "weak" combat efficiency icons on the map.
Those icons are optional, so you may disable them to ramp up the difficulty (only Gold must strictly be hidden, Icons are up to you).

As you cannot check other nations, you may activate "Alliance Map Mode" in the Bottom Row to check if a neighbor has allies before attacking.

And of course, smaller nations are harder to win with than the bigger ones. However, with patience and a bit of luck, even a very small nation may win as long as you time your attacks right.

Last tip from me: pay attention to your Revolt Chance
Don't go on an all out war with 3 of your neighbours just because you have a high Combat Efficiency. It will only come back to bite you soon enough.
It's also why you are forbidden from using wars to death, as regular wars force you to stabilize your nation to prevent rebellions