Does it give them increased attack or defence or does it just make them harder to break?

The reason I ask is because the AI armies always seem to turn tail and run at the drop of a hat. I don't want to give them an unfair advantage stat wise but I would like them to put up more of a fight before their entire army chain routs and the battle ends despite 80% of their army still being alive (well not for long once I've finished chasing them).

It may make for longer battles too.

So would upgrading all units morale a couple times or more really help them just last longer before breaking or would it have other effects?

Would there be a way of even changing it so that only the AI would get such a bonus to all its units or would I need to give it to all units individually including my own?

Sorry if this is the wrong forum, its a general enough question I think.