Check out Snipafist's Strategic AI and Balancing Mod.
Greetings all, I've polished up my own personal mod enough that I feel it's ready to hit the streets. It is mainly a series of changes to the export_descr_units and buildings files, but also some minor changes to the descr_events and descr_strat file. I'll run through all of what I did and explain why, and the download link is available at the end of the first post.
The primary inspiration for this smaller mod was to solve some of the balance problems in Medieval as well as slow the game down a little bit. Getting the AI to recruit decent armies was also a huge incentive, and I've actually succeeded in this area. Let's go on to the laundry list, then:
1) Farms. Farms now offer +X free upkeep slots as well as +X to food production. The ideological reasoning was sound - the more developed agriculture was, the more landed serfs and freeman farmers one had control over that could be levied, and the more militia troops could be easily fed. The game balance rationale here was twofold - castles needed some buffing, and farms needed an incentive to be taken in cities. By upping the free upkeep limit as well as upping farm production, they're actually competitive choices now for either settlement type. Obviously, castle troops needed to include some "free_upkeep_unit" units now, so I gave them a SMALL smattering of units that they can support for free. The units in question had to be lower-upkeep generally early units that were included into forces with little to no training. Peasant troops were obviously in, as were enslaved troops (Nubians), and naturally proficient conscripts (like Spanish Javelinmen and Egyptian Desert Archers). The following castle units are "free upkeep" now, provided you have the farms/tourney fields to support them:
peasants, peasant archers, peasant crossbowmen, javelinmen, levy spearmen, highland rabble, woodsmen, Nubian spearmen, Sudanese Javelinmen, Turkish Javelinmen, Azabs, Desert Archers, Nubian Archers, Lusitanian Javelinmen, and Slav Levies. That is all. No mounted troops are supported whatsoever.
2)Castle Walls no longer provide any troops past the basic 2 of the lowest-tier cavalry. Any units only previously available from castle walls has been moved to the corresponding barracks (if dismounted) or stables (if mounted) choice. Stables were being completely overlooked and when they weren't being overlooked, they were cavalry spamming with a 7+knight-strong recruitment pool. The madness had to end. To compensate, castle wall upgrades will now always provide +1 recruitment slot over their predecessors, maxing out at 5 recruitment slots at a citadel. This ensures that castles remain excellent unit production centers no matter what stage of the game the player is in.
3) War machine and cannon recruitment buildings are now city-only buildings and cannot be taken by castles at all. This represents the required pool of skilled freeman craftsmen not available in a city. This also effects how the AI recruits, which I'll get to later.
3a) War engines now have a pool limit of 2, but come 50% larger (3 engines rather than 2) and at 50% greater cost. This makes them worth the army slot they consume, and affects how the AI recruits as well. The only exception is the Monster Bombard, which only had one cannon, which I have doubled to two at a 50% cost inrease. The reasoning is that one monster bombard was adequate enough on its own to tear down defenses before, so two is overkill. Charging twice for unnecessary extra force is redundant, but a cost upgrade was warranted to keep it in line with the others.
4) Later wall upgrades, namely the large and huge city walls and the fortress and citadel castle walls, are now time-dependent. Large city walls and fortress walls are available 100 years past the start date at 1180 and the huge city walls and citadel upgrade are available 200 years past the start date at 1280. I have done this to intentionally slow down the game slightly, as well as give lesser factions a chance to "catch up." It is incredibly difficult to support a large empire if you do not have the highest level buildings, so expansion must be kept moderate and the corresponding units will also be kept reasonable. To a certain degree, you (and any rich AI factions) are forced into the same era as your competitors, so you cannot turbo-money your way up to late-game elite units and simply destroy the AI's still-early units. The noted effect of this change is pretty great, and I think it adds a lot.
5) Gunpowder's discovery has been pushed back to 1280 as well. Gunpowder weaponry started appearing in earnest around the early 1300s, and I thought having mid 13th-century cannon duels was more than a little ridiculous. This dramatically inreases the useable lifespan of basic wood-constructed siege engines and makes it harder for players to blitz through the AI earlier on.
6) Merchant income was increased fairly strongly (roughly 2-3x as much as vanilla). This isn't unusual, and is typical of most mods. This is good because it makes merchants useful for you, but also because the AI likes to have a large number of agents and otherwise its merchant-recruiting is simply a liability. Now it is an advantage.
7) AI "personalities" were almost all changed. The vanilla personalities did not encourage the AI to build armies that maximized its advantages. Further, all "caesar" and "stalin" AI personalities have been removed, as they caused the AI to over-recruit siege engines to an insane degree (armies of roughly 1/2 siege engines were not uncommon). Changes have been very noticeable. Eastern factions now recruit armies heavily based on cavalry with great archer support rather than a load of crappy infantry, for example. Scotland is a swarming menace if it gets rolling. Try it out and see!
8) Changes to the AI's army composition are greater than the sum of their parts. The AI is set to a military build policy. This is smart because it means the AI is always trying to compete militarily with the player so as to discourage being rushed too early. This is stupid because it keeps the AI always recruiting out of everything it can. By giving castles a recruitment boost and limiting siege engines to cities only, I've seen armies composed of almost entirely castle troops with the occasional siege engine or militia unit for support. Previously, the AI made more militia and far more siege engines (remember that both castles and cities were cranking war machines out) than it needed, so they were thrown into poor armies to simply get rid of them. No longer. Further, the AI's building choices are no longer stupid - stables are necessary to compete in terms of cavalry and farms are good in cities due to their free upkeep slots. Further, because of building limitations by era, the human player has a hard time getting an immense lead over the AI, making battles more challenging. Finally, because the AI now recruits more intelligently for its faction strengths, the armies you see are far better.
9) Increased movement. I increased base movement points from 80 up to 100. This is not enough to significantly change movement, but it is enough to get the AI to succesfully combine stacks/surround your armies when it needs to. Of course, it still has the occasional "six tiny stacks" problem, but the incidences of this are much diminished.
10) Minor character changes. I use the MEDIFIX character traits mod, with a couple small changes - I included some base princess triggers so they're not all hideous Gorgons, included Orthodox Bishops (which I imagine must be an oversight), and a couple other minor tweaks. Note that generals governing a city a significant distance from the capital can become increasingly discontent and may even rebel! This means that any player trying to conquer the world must have wise capital placement and wise useage of loyal (and probably chivalrous) characters for your far-flung cities. This creates an additional brake on acquiring a super-empire easily (and is characterful and fun), but isn't likely to happen too often if you pay any attention.
11) Diplomacy. I use a slightly modded version of Shaba Wangy's infamous 1.4 Mod. Works like a charm. Enemies typically behave sensibly (obviously not perfect, but better than anything else I've tried as of yet, including the Ultimate AI mod) and there is enough war to be interesting (factions do in fact wipe one another out without your help) without it being insane. If you are not defending yourself properly, you WILL be attacked, but you can cultivate trusted alliances if you're attentive about it.
12) Unit balance changes. I tried to run with a light touch here, but I feel the need to create a sub-list to explain what I did and why.
-Conquistadores are now available out of castle stables once the "world is round" event occurs. It makes no sense to defeat Aztecs and THEN start recruiting Conquistadores. Use them against Europeans ahistorically if you wish.
-Cossack Musketeers have been moved to the city royal barracks and replaced basic Russian Musketeers. It was simply too good to get musketeers 100 years before everyone else off of your walls.
-Ottoman Infantry now have good stamina. This encourages them in their dual role of decent archer/decent infantry. Previously they just get tired too easily.
-Dismounted Polish Nobles had their stats raised to make them comprable to mounted Polish Nobles and the cost increased accordingly. Now they're worth recruiting.
-Strzelcy and Mounted Crossbowmen ranged attack upped to 7 to make them worth taking.
-Hussars given a fast mount to make them worth taking and to fit their description.
-Nubian Archers and Spearmen given good stamina to somewhat encourage their use, as well as being "free upkeep" castle units. They're still pretty poor compared to units that come before them, though.
-Men at Arms are now upkeep 175 because they weren't competitive with Italian knight choices whatsoever before.
-All two-handed non-pike weapons (greatswords, great axes, halberds, etc.) are now armor piercing. That's what they were made for, and otherwise you've got units that just flat-out aren't useful.
- Byzantinian Spearmen were given a bit of a boost to make them slightly better than basic Sergeants, but worse than Armoured Sergeants, much like the other Eastern European spearmen. Otherwise there was very little incentive to build a Byzantinian barracks at all, and Byzantinian cities were remarkably weak against a mostly-cav siege assault.
-Kataphractoi had their armour increased by one point to keep them competitive and because it makes sense when they're completely covered in it.
-Camel Spearmen upkeep reduced to 250. Determined Moorish tribesmen on camels do not cost more to upkeep than European knights, thanks. Encourages their use as a niche unit (anti-cav cav).
-Azab defense skill raised to 4, attack raised to 6. They're still god-awful, but at least they're conceivably useful as last-ditch castle defense infantry.
-Zweihanders available at Barracks level rather than Armoury, as their armor rating is consistent with that level and Dismounted Gothic Knights (which are now available at the Armoury) are superior and fulfill the same role.
13) Explorer's Guild now produces effects. It is supposed to produce higher trade values and a faster movement rate and did not. Thus, I have given it the "road_level_2" ability which converts the roads in its province to highways (granting faster movement and better trade), and trade bonuses of 1 and 2 for the Master Guild and HQ guild, respectively. Works like a charm now, and it's a guild you actually will wish to pursue in sprawling provinces or landlocked trading provinces (like Dijon). In terms of raw trade value, merchant's guilds come out on top because of their merchant-augmenting effects and lesser cavalry recruitment, but the Explorer's Guilds have their place now.
14) If anyone wishes to include any of the tactical AI mods (sinuhet or darth) or horsearcher's wonderful sky mod, be my guest. I felt I only needed to include what was necessary to produce the balancing and AI-augmenting elements.
And that should be it. Let me know what you think of it!
Installation instructions: simply drop all the files into your "data" folder, with the exception of the descr_strat file and the descr_events file. Those must go into your data/world/maps/campaign/imperial_campaign folder. Make sure you've created backups of the relevant files and that you've unpacked properly and are either using a mod switchover or the --io switch.