After starting and playing several English GA campaigns, I decided to start a conquest compaign.
I use very aggressive tactics as the English, and attack most of my neighbours, starting with the French. This may sound ruthless, but it is my experience that the AI picks a fight with you even if you're allied with them and haven't wronged them. So I might as well be the one to start.

When I started the conquest campaign, I used the same tactics I used before in my GA games. Immediately attacking France, Killing off Aragon (and if I get the chance Denmark), and reducing borders with the HRE.
I do this because if I don't I'm left with hard to defend French lands which Aragon, Spain and HRE will attack anyway.

My question is this. Is the "campaign AI" even more merciless towards you then the "GA AI"? Because almost immediately everyone started hating me (not so surprising I admit) and attacked me as soon as my territory/ship was in sight. My only allies are the Spanish now, but I know from the past they won't let up a chance to attack me as soon as I leave Aragon.
In my GA games I was far more able to blitzkrieg my way through Europe without everyone declaring war against me.

I guess it will make this game even more challenging.

My other question is how much the AI gangs up on you. I've found as the English my neighbouring factions are quite peaceful. This is striking to me as when I'm playing as another faction like the Hungarians, other factions are much more inclined to war.
HRE rarely attacks anyone when I play as the English, rarely they only go after the Italians. Italians never attack anyone when I'm as the English. The Polish will rarely war with the HRE, as will the Hungarians. The Danish never attack the HRE. The Sicilians will rarely war with anyone other then Byzantium for Naples. And finally, and most surprising, the Spanish will always ally with the Alamohads!
This leaves my neighbours with enough troops to garison at my borders. Not that it will save them but I do find it striking.

I guess the AI asserts the player's threat correctly or something...