Combat vs AI is extremely easy in this game because the AI doesn't have a clue. I play immortal and beat the AI easily because they simply throw away all their units. Watch Sidon's Youtube videos for how to destroy AI units on Deity. I think there are many simple changes to the AI that could be made to improve the difficulty of combat. Here are a few: 1) Prioritize ranged over melee military techs. Get crossbowman, cannons, artillery before infantry. 2) Don't send units into enemy territory if you see more than one or two enemy units. They will simply be eaten up by enemy ranged. 3) Don't make that many melee units. A good ratio is probably two to three ranged to one melee and/or one horse unit. 4) Use citadels. When you have extra great generals, put a citadel into the territory in which you are attacking. It doesn't really matter where (OK it does, but any use is better than no use because citadels provide huge bonuses and because extra great generals come frequently). 5) The AI withdraws from combat way too early. If you send in some units and they are damaged, you have committed yourself to the attack. The AI should press forward rather than withdrawing and allowing additional damage from my ranged. These are a few easy changes that would make the AI much more difficult from a combat perspective.