Played a 1.1d game looked good. All that 0 hp stuff is gone.
I played normal world, and 10 challenging AIs. Umber got stuck. He built a bit too far away from the farm. His ZOC eventually covered it but he didn't have any materials to build a farm (confirmed by attempting to trade). He had spent his 10 pop on a tech lab and an arcane lab. So he wasn't gaining any materials either. I have him 5 or 6 mats and it unstuck him. ie he built a farm. Then houses, then was able to get rolling again. Always get at least one workyard.
I whipped my closes neighbor out fairly early because they build their second city right where I wanted too and there was no way I was going to let that stand. I took it easily with my sov a hero and a few early staff guys. I held it until I had some spears units and geared my sov & hero. Then I took the enemy cap.
I saw a couple factions whipped out. Umber (who was stuck for so long) and one other. Altar had about half the map under their ZOC by midgame. Altar should have rolled everyone. They had most of the metal on the map. I had one crap iron place giving me 1.
When I eventually started steam rolling with my sovereign and his son maxed out altar had all old units. I think they looked at thier combat scores and thought they were ok so weren't building anything good. They were obliterated. Altar should have been steam rolling everyone with their sheer size.
Small short wars might actually be very good for the AI. Losing old units in battle will have a cleansing effect. The combat numbers to calculate its miltary health with more recent units means the numbers will be more realistic predictors of actual military strength. If they have alot of old units its military health data is stale.
Perhaps the AI should look around across the border and examines the most powerful unit the enemy/allied has that it can see. Call that unit the the cutt-off point. Any of its units that would do zero damage on average to the should be marked obsolete. Obsolete units should be destroyed one at a time and replaced with a more modern unit assuming there is one. Once all the obsolete units are replaced recheck the area for a new super unit. Mark your obsoletes and begin replacement. This calculation only has to be done once in a while when all the old obsolete units are replaced which may take many turns.
Aggressive personality AI's might go for short wars rather than cycling the troops out. Loosing the crappy troops taking a city. Then being eager to sue for peace, and consolidate its gains. They take a city and say "Your city was build on grounds considered holy by my people. Now that the lands are back in the rightful hands, I will consider a truce if you pay me 100 gildars."
The combat values assigned to armies is only valid if the two armies are in the same ball park of technology. This is one way to help the AI not be lulled into believing its better off that it really is.
Overall I found "challenging" to be too easy. I'm going to bump the AI's difficulty back up to hard. That seems to be the sweet spot for me. The ai was doing some good stuff and blocking the one man wrecking ball technique with my sov.