The AI just doesn't use armies effectively and it's a problem. Where to even start.
Formation: AI loves to form their army deep inside friendly territory. Often they'll invite Lords who are already on the front lines, who then have to travel to the rally point, then travel back. Major waste of time, and it's not at all uncommon to see them already under 50 cohesion by the time they even see an enemy.
Targeting: They're still terrible at picking appropriate siege targets. Example; Southern Empire will be sieging targets halfway down into Aserai while completely bypassing Husn Fulq and Tannuh Castle. Over the course of three wars. Not helped by the previous issue where they spend a week forming the army by Poros, then start marching straight for Quyaz and running out of cohesion and disbanding before they even get there.
Other examples: Northern Empire targeting Balkathand despite Khuzaits holding several of their castles by Amphrela.
Worst example by far was Southern Empire declaring war on Sturgia (which shouldn't happen anyway) while at war with the Western Empire. Rhagaea gets together 1,500 troops and marches on a random castle in Sturgia, all the way through an intact Northern Empire, while the Western Empire absolutely ravages the South.
Siege Mechanics: Lost count of the number of times I've seen the AI arbitrarily abandon a siege to go patrol around a random village or something similar, to the point where I recently watched a 500-man army break off an assault on a castle with 50 garrison when only 7 enemies were left. They just packed up and decided to head all the way to the other end of the kingdom. I have also seen armies that size besieging castles with literally zero defenders and waiting to build a ram and a siege tower.
Reinforcements: The AI will recruit from towns and villages in an army, which is good, but there should be a certain point where they'll cut a Lord loose to go recruit on his own if he's down to 4 troops. They should also look for new Lords to invite periodically, because it seems like they only ever have the Lords they start with and that's it.
Suicidal behavior: An army really needs to know when to call it quits. Seen 5-6 Lords in an army with a handful of troops each run deep into enemy territory to raid a village and get taken out and captured by one full-strength enemy party.
