Everyone wants to kill me..

[Fexas]

Playing as france M/M trying to comlete short campaing.
Need only 2 more cities.
Enemies HRE and milan. Reputation is Very reliable, amiable relationios with almost everyone and suddenly I'm attacked by Portugal, Denmark, England, Sicily, Moors, Scots and Pope () in ONE turn!
Sicily, Moors and Denmark even were my ally. Why the hell they want to kill me?

[TheEmperor111]

It is the Ai But maybe it's hard coded in somewhere that when you are close to winning that you are attacked more??? It would be interesting to see someone try and prove this.

The Emperor

[Vipman]

I think there is some random thing that makes AI attack the player eventually, I'd bet if you reload a few times, a few times it might happen again, some other times no one will attack you. But by reloading it's just delayed anyway.
I think the main factor that increases the chance of factions attacking is the amount or regions the player has. The more, the higher chance.

[Highlander of Scotland]

it is just the AI, it is dumb. Allies will regularily betray u

[Duncan III]

It makes sense really, you can't expect the ai to do what you want it to do all the time- why should the other factions just let you win?

[Drustan]

For the Pope to have attacked you, you must have done something to piss him off big time. If the Pope dislikes you, other factions can appease him by attacking you, hence why all the Catholic factions are ganging up on you.

[Kaiser Nonsense]

No, the AI isn't dumb, I used to think that as well, but then I learnt it is very well developed to make the game hard enough, it all depends on your trade rights and relation with other factions, for example you are allied with England, England is at war with France, you have trade rights with France and good relations with them, it's likely England will betray you. You need to stand for your allies, fight their enemies, ruin your relations with their enemies and stay loyal to 'em, also, if you are catholic, highly avoid having good relations with muslim factions, especially being allied to 'em. As for the Pope, like the mate above mentioned:

For the Pope to have attacked you, you must have done something to piss him off big time. If the Pope dislikes you, other factions can appease him by attacking you, hence why all the Catholic factions are ganging up on you.

[King William the Conqueror]

By default AI will target the most advanced player. And since humans are better than they, they will target you.

[lolIsuck]

The other factions are always looking for settlements to capture, if you have a small garisson in a settlement and they have a larger army nearby it can always attack. The AI is very opportunistic and doesn't care much about diplomacy (unless you're on very good standings with a faction, it can still attack but not that often.)

[shikaka]

The other factions are always looking for settlements to capture, if you have a small garisson in a settlement and they have a larger army nearby it can always attack. The AI is very opportunistic and doesn't care much about diplomacy (unless you're on very good standings with a faction, it can still attack but not that often.)

This is my observation in general as well.
Also, this "opportunistic AI" cannot really make plans: it just sees a dock with no navy nearby and blockade, not taking into account your 5:1 advantage in land armies.

[Aeratus]

The AI in the vanilla grand campaign does have a tendency to betray you, but generally this happens if your relations is low. If relations are high, they are not likely to betray you.

In contrast, the AI in the Teutonic campaign is hard coded to betray you once you have reached a certain number of provinces.