Battles of what size? How recently?
Does size really matter? If there are battles, there is bound to be some frustration created. Nobody likes losing. Be it the battle itself, or some men, or region damage.
Time obviously does matter, though. A bonus could be done proportional to the size of one's army and fading with time. For example, if the fade limit is one month, and a realm had 10 000CS total, then having a battle with 5 000 CS would grant a +.5X bonus to recruitment (X being whatever factor deemed balanced), which would fade to being a mere +.25X bonus after two weeks, and +0X bonus after a month.
Because as I said above, even if two rulers agree to "game" this for their purposes... it will end up pissing off some of their nobles. And even if it doesn't... the losses of war are likely to compensate the increase in recruitment, so why bother "abusing" this?
