Campaign/Diplomacy AI

[nikolai1962]

CavalryCmdrThe AI behaves differently toward the Slave faction then other factions, any invade type toward the Slave faction will result in attacking as soon as they think they are strong enough. That said, Invade buildup is an agresive stance, and even on buildup the AI will attack other AI factions if they are overwhelmingly powerful. Much like invade immediate will build up thier forces if they are weaker then thier target. Unfortunately the AI will also have a tendency to lauch raid type attacks while on buildup if they do not have more pressing concerns. The best patrol-type defence I've found is invade none, defend deep toward neighbours and invade start, defend raids toward non neighbours. Problem here is they have a tendancy to not intercept invading armies, however they will concentrate more on building thier infrastucture while still recruiting a reasonable amount of troops.

The ai_db.xml only gives the AI a general 'stance' toward other factions, it dose not actually control the AI, so any invade type besides none is an agresive stance and can result in the AI attacking that faction. This is where manipulation of invade priority is very helpful, the AI will not invade a faction that has a much lower invade priority then another faction. For example if the ai_db gives an invade priority of 1000 toward slaves and only gets up to 400 toward everyone elts they will not attack unless invade_opportunistic is used, even if the only slave setlements left are the ones in america.

Mine may be working out a bit different because i currently have all the invade priorities mostly the same so the final priority is heavily influenced by faction standing and global standing and the factions just dislike the slave faction more than anyone else at game start. With mine it "seems" that the invade_buildup setting has a specific pause built into it to allow armies to merge. It may just appear that way though.

What i was mostly doing is trying out the defend settings with a view to how well the AI armies are merged when the faction is at peace with everybody. Usual caveats about how recruitment, unit costs etc may affect different mods but i set all the defend decisions to be the same just to look at the merging.

Pretty much replicates what CavCmdr says in his page linked at the top and fits what you'd expect but reproducing results never hurts so...

defend_deep: ok merging (a comparison would be 3-4 stacks of 3-4 units instead of 7-8 stacks of 1-2 units), heavily weighted to the capital or some other central spot they decide on, good garrison in the capital, not so good elsewhere.

defend_fortified: ok merging, less weighted to the capital so they try and cover more cities and more of them have ok garrisons, big downside is the actual forts they build and the armies staying in them forever. not a problem if you don't mind losing forts but i'd like to avoid doing that if possible.

defend_frontline: ok

normal and minimal: pretty useless purely from a merging point of view. The AI doesn't seem to try and merge with these settings.

advantage of deep is you can expect a big counter-attack stack if you invade. disadvantage is in a faction that is physically large--in terms of area, the counter-attack will take a long time to arrive. fortified is more likely to have a stack on guard but because the AI is trying to cover more places they are likely to be smaller stacks. So overall, purely in terms of defend decisons and merging/garrisons, defend_fortified would be best if it wasn't for the fort glitch.

Also, geography seems to matter with defend_frontline. In areas with a lot of narrow mountain passes etc the AI seemed to have bigger problems merging.

However, seems to me though that the majority of the AI's army merging happens as a result of the invade decisons. So currently i'm thinking that's where to look if you want to get the AI to merge more.

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Ran through it quickly again with the default invade mode being invade_start instead of invade_none. This had a lot of interesting effects. Probably confused the AI a bit too but overall this seemed to increase the average level of merging with each setting. They also seemed to hold back a lot more e.g my french faction has 4 starting cities and armies and normally they'd all move out and attack a rebel city each on the 1st/2nd turn with invade_immediate or 2nd/3rd turn with invade_buildup. With invade_start set for all the other factions what happened was two of those starting armies moved to the capital, merged and waited, while the other two did the rebel bashing.

Worth experimenting with maybe, bearing in mind the points CavCmdr makes about it starting wars you may not want. I'm thinking of maybe randomly switching the AI between invade_none and invade_start with neighbouring factions they're at peace with to see if i can trick them into merging more.