How does the AI in M2:TW compare to R:TW?

[Rex Somnorum]

and Sweboz hookers (Back then there was no ID; so the more hair, the better).

I'm useless at modelling, but I could certainly script in some modified princesses, if you need help.

Is there any evidence the two actually interact in M2TW? Does the AI respect a ceasefire and alter what it's doing, or throw whatever it has at you as soon as it can build up an army again?

I spent half an hour typing out an in-depth answer to your questions and suddenly my connection timed out. Once more unto the breech.

I'll be concise: yes. Keep in mind, though, that a faction with bad relations with you will probably violate the ceasefire after re-building their forces, unless another faction distracts them. But that's only natural.

That is also reassuring. Is it possible to effectively stop naval invasions if you strongly garrison coastal settlements?

As a side-question, were the factions landing troops those you were actually at war with, or had something to gain by invading? The problem with the naval AI from RTW:BI was that anyone on the same body of water was a potential aggressor, regardless of diplomacy status (because of course, military and diplomacy AI didn't talk to each other in RTW...).

To the first question, yes but it's expensive. The second question is a bit more complicated. Yes, they both had quite a lot to gain, especially since my armies in the theatre were generally weak. However, the decision to invade is balanced against the target faction's standings (global standing, or reputation, and faction standing, or relations) and risk. The Byzantines viewed Egypt - an ally of their nemesis, the Turks - as a weak and obvious target. Portugal is essentially sandwiched between two continental powers - the Moors and Castille - and take to the sea seeking Lebensraum. So, even though the English and Portuguese might have lukewarm relations, the rewards of a successful invasion far outweigh the risk. In some cases, the AI seems to behave irrationally when it is operating on a logical game mechanic. For example, Poland may start a war with Russia by blockading Russian ports simply because their navy is too weak to defend their trade-lanes, the lifeblood of the Rus' treasury. Basically, neutrality means nothing, standing means everything and weakness will be exploited. A close ally will likely remain a close ally. But neutral factions are wild cards.

To be fair, I've developed a theory base on my trawls through the descr_campaign_ai_db.xml file that the game has hardcoded "enemies" - or factions that will always remain rivals, which would explain a lot of the AI's behaviour.

On an endnote, the AI can be vastly improved by altering a few values in the game files. There's one line in the config_ai_battle.xml file that's massively powerful:

<friendly-to-enemy-strength-ratio>0.8</friendly-to-enemy-strength-ratio>,

this measures the balance of forces to determine whether an army should attack another army, on the campaign or battle map. In Vanilla, an army needs to be only 80% the size of an enemy's force to attack. By increasing the value to, say, 1.5 the AI will only attack with a 50% numerical advantage, which would eliminate most of the small-fry offensives.

By the way, why doesn't the medieval period interest you?