Hmmm... was playing as the Dov on Emp.
Yea, don't count on the partner AI on doing too much.
Yep, what I did was to rush for the first chokepoint Bannor city in the hills. Its heavily fortified (and well on a hill), but once you crack it, you basically could stop the tide of Bannor troops from your ally.
You start with Construction, so dragging over a decent amount of siege for collateral damage could quite easily crack their defenses.
The war against the Lanun and the Grigori doesn't start till you sack the Bannor capital, so if you wanted to, you could take the opportunity to train up a few veteran units in preparation for the Lanun campaign.
Furthermore, the Lanun tech rate should be by far slower than yours (since you had the new Bannor cities as well as an ally which helps to contribute some beakerage)
The Grigori was very advanced and strong, but you do have the advantage of being on a separate continent (and you know how lousy the AI is at cross-continental invasions). So you basically have a very secure swath of land with only the new Lanun cities possibly under attack.
I suppose I finished off the Bannor and Lanun pretty early on so I didn't see the 100 turn mark even as I completed the campaign.
However, I did have some trouble with the Grigori navy at first, and they had frigates pretty early.
But since your interior is secure and the Grigori hardly landed any units on our side, I was able to slowly (um... ok I did pay and rush some extra frigates out) build up your navy to rival his--then slowly sink them.
Since you're playing the Illians you should definitely head for Theocracy to get snowfall on your 3 priests. With them you would be able to do massive AoE percentage-based damage to all surrounding units which are priceless.
With such power on your side you could seriously consider doing an amphibious assault on the Grigori coastal cities--Snowfall from your ships, then attack their weakened defenders right from your boats. This keeps your units perfectly safe from counter-attacks once you have secured naval domination.
After that its simply draining the Grigori army of their units while they rush to defend the city--don't take over it too quickly lol, keep the siege up to drain all their tier 4 adventurer units before you take it, and by then your units should have so much experience that simply wading through the remaining green dragon slayers to their capital shouldn't really be that difficult.
On the Doviello side, I wasn't "lucky" enough to be able to enjoy the High priests, and I went RoK for Mines for early iron to kill off the Bannor fast. But I suppose I was able to knock the Bannor out quickly due to the upgrading of melee units on the field as I captured workers and conscripted them into my army (with RoK successfully funding my promotions so I could keep tech at 100% till late on). There was where I found the slight reported "problem" of having both copper+iron weapons when I upgraded my workers to warriors then to axemen--so I was having extra +1 str on my ironed upgraded champions.
The Lanun wasn't posing much of a threat once we declared war on it, and actually the Illians were doing a respectable job at keeping them them at bay and actually taking a few cities, since I gifted them the extra iron from my Mines, and I teched Machinery early for the War Machine and the Illians benefitted from having really strong ironed Crossbowmen.
The Grigori however, as I mentioned had an army way larger than mine (but I think since they were at peace with the Lanun they didn't even bother landing through Lanun territory to attack me). Once the Lanun were dead I had to take some time to build (or rather rush out) a frigate force to counter the Grigori's powerful navy.
Then I had to actually take on the massive Grigori army on land. Their powerful Adventurer berserkers took a pretty harsh toll on my army initially, but I was able to bait them into attacking me on a hill across a river, where my crossbowmen took care of them.
After the adventurers it was just a matter of mopping up the rest since the Doviello had the luxury of having a powerful 19 str War Machine, though I still had to bombard cities with siege to weaken them before it rolled in for the kill.
As I mentioned in the Scenario thread, I was thinking of slapping Auric for making me go through so much trouble against the Grigori when I already had a level 15 War Machine and could just go looking for Brigit instead for her blood =D