Trespassing and the AI
I find it quite frustrating that the AI keeps trespassing my territory when a bunch of its units is stuck behind my borders. I understand the reflex, but it's totally annoying that I have to tell the AI turn after turn to leave my lands. Right after leaving the AI just moves its units back into my territory and it's rinse and repeat. Besides that on large maps you really need to zoom out every turn to check if there's not some sort of AI player in your territory. It's a wast of precious gametime.
In other games trespassing means war unless you sign an open borders agreement. There is such an agreement in FE too (can't come up with the name), but besides that tresspassing doesn't mean war or have any other repercussions.
I really would rather see this 'feature' leave the game. To pass on other's territory there has to be an agreement, otherwise no way to cross the lands so you either have to go to war or to 'buy' yourself an agreement.