@Hawkwing I think this would fit in your little ideas you posted sometime ago.
We all know the AI in FE isn't that smart. Green units are suicidal, red enemy units are too and will keep attacking after it's obvious they're done for. Difficulty boosted modes rely more on giving the enemies skills and more enemies than anything else. What if the AI was changed depending on the country/faction the units belong to? Using Tellius and Fodlan as examples.
Begnion/Adrestia: They bring along ballistae, fire orbs, expensive weapons and war devices. They fight dirty, but will run to healers when wounded.
Crimea/Faerghus: Protect the leader, wall of swords/spears to do so, if the leader falls they either pull back or panic.
Daein/Leicester: Sneaky tactics, protect the leader, mostly hit and run though.
Gallia/Duscur/Almyra: Power through everything in their path.
Kilvas/Phoenicis/Brigid: Hit and run tactics. Healers are stationed on the outskirts, for the bird laguz this would simply be one with a bunch of vulneraries to give out.