diplomacy quirks

[Seravy]

but instead a stack was created near Merlin's fortress, then it would look at his home continent. It wouldn't find any valid path to any enemy target, so it would decide that continent to be an invalid target.

Yes, and it will
-Head to the shore if it's a land stack, then board a ship and get transported to the main action continent
-Head to the already selected main action continent directly if intercontinental but in this case it would find a path (which doesn't stop the other, land stacks from marking the continent invalid anyway, as soon as this stack steps on a sea tile.)

Additionally, it would have to designate one of the other 4 continents as the main action continent.

Yes, although this happens way before the home continent was marked invalid, as it was never a valid selection anyway.

It would do this based on both presence of enemies, and presence of his own cities.

No, this is done based on the presence of enemy cities and the number of tiles the continent has. It's random but it has heavy weighting in favor of the primary enemy (blue).
Arnuz's continent has the most blue cities and the most tiles of land so it has far more chance to get picked.

Once it arrives, it then looks for a target on that continent to attack, based on defender strength and distance from the stack, and maybe a modifier to prefer the primary enemy? Since the stack is coming from the east, distance will put most of Arnuz' cities much closer than either blue or red; Arnuz' cities are probably also more poorly defended.

Exactly.

[Arnuz]

Thanks for the explanations, this sheds quite some light on the issue. However, I am still convinced that there's an issue hidden here.

1. Twice, the doomstack with a hero came to this continent. Probably recruited, but the AI didn't crack any lair on the continent I had intel on, so even if they were prisoners, they come from the other continent.
2. The stacks are all wave walkers/flyers, ships aren't a consideration in this case. So even assuming that the stack starts going towards the enemy, then decides to go against a player he's only aggressive against (which IMHO is the strangest part), it means that the stack did something like this:

White path planned, light blue "deviation"
... This means that even under the assumption that it was going towards the westmost blue target rather than the red one, starting from the westmost city - which isn't even the capital IIRC - it's gone to a city further away than the closest target. I believe that there's more under the hood here.

I mean, this could all be down to the issue that the AI cannot gather intel and therefore, a neutral city with a small force will attract it half way the map, despite the presence of closer targets, and despite an ongoing war. The main issue that I see with this, is that it wastes a lot of turns! This stack for example was speed two thanks to the sprites. If we directed doom-stacks towards closer targets I believe we'd be making a service to the AI.

On the other issue, I find that sending forces against a neutral while being at war is quite questionable, when the other party might be concentrating all of its forces towards you... Might this be the reason why AI to AI wars often seem inconclusive and rather fake?

[Seravy]

   

Assuming the AI summons Sprites into that city on your continent and its own equally, the doomstack will be gathered at the point marked on the map with the white circle.
From there, it can attack up to 10 tiles, roughly the red square. So it can either attack that blue city, which is far too well defended for sprites, or your green city. If it doesn't want to attack either, it'll be forced to go towards the main continent, which is yours.

I believe that there's more under the hood here.

The blue city when I checked, it had 3 klackon halberdiers in it. That's not much, but I suspect this was a neutral city recently taken, which originally contained like 6-9 wolf riders. Otherwise, it would have gnoll units in the garrison, and more than 4.
But even if it's "only" 3 klackon halberdiers, each of those are 40 military power while sprites are 10. A hero without equiment isn't strong either. There is no way the stack can attack it. Especially not in the previous version where the defender was counted twice.

...that doomstack looks formidable, but it has less power than 3 halberdiers...you guard your cities with less than 3 halberdiers, the AI uses more. So they cannot be attacked but you can.

Might this be the reason why AI to AI wars often seem inconclusive and rather fake?

No I think that had something to do with the casting skill bug.

[Nelphine]

AI wars definitely make a huge difference. However, AI tends toward very strong garrison's, with offensive units made up of scraps leftover after the garrison's are strong. (This was one big reason for the development of doom stacks). But one big side result of this is that the offensive stacks tend to see the opposing AI offensive stacks as valid targets far more often than important targets like cities. So while the AI actually do kill off a fair number of each others troops, regularly territory doesn't really change hands.

Then we added doomstacks. Since this actually results in strong offensive stacks, especially in the mind of the player, its natural to assume that this should result in more meaningful battles between AI. However, there is one big flaw in this. Doomstacks must be intercontinental. This usually means fliers. Fliers generally are weaker stat wise than non fliers (that's how eflying is balanced). But AI don't fight tactically. They fight with strategic combat, so only raw stats matter. So the doomstacks are often much weaker in the eyes of the AI than their targets.

This is most especially noticeable early game when 2/3 of the AI are using sprites. And for you arnuz, early game is the vast majority of your experience.

[Seravy]

Agreed, a "doom" stack isn't very doomy until the AI has at least uncommon flying summons, and a large number of those don't come that quickly. Sprites are by far the weakest summoned unit in the game - roughly as good as a swordmen unit.

[Nelphine]

Why did a peaceful AI with half my army strength declare war on me? (He is allied with 2 other peaceful allies, but neither of them were at war with me. He told me I was expanding too much.) On the same turn an aggressive theurgist with 1/3 my army strength declared war on me, also because I was expanding too much.

[Seravy]

Was your relation with them falling below the -40 line? (Restless ->Tense)
If yes then you triggered that type of war declaration.

But if they said you are not listening to the warnings then it was because you failed the "repeated warning roll". If you trigger warnings from AI consecutively (like, more often than once every ~10 turns), the second and later warnings have a chance of war which increases with the number of accumulated warnings.

I think these two are the only possible options here.

[Nelphine]

Hum. Both AI have me 2 'you're expanding too much' warnings prior to that (always on the same turn). I don't remember exactly how many turns was involved. On the very first warning, all 4 AI gave me the same 'you're expanding too much' warning.

Relations, could have been around that line for the two that declared war on me? But always neutral with the other two.