[aldin]

Fearun,

I'd say a lot depends on relative strength. Depending on the exact situation I'd use one or more of the following:

a) Buy a Merc army to hunt the AI army down.
b) Summon an army and send some researchers on temporary (permanent if you replace them) assignment as commanders.
c) Wait in fortifications until a sufficient force can be recruited.
d) Buy defense.
e) Attack the AI's territories.

I like a combination of a&b usually then replace the researchers by buying new ones. One tactic to remember when AI hunting in your provinces is that the AI tends to go after the richest, least defended provinces.

~Aldin