In the Vrynenwood, the leaves are not what they seem.
When an opposing army brings in the big weapons, your kingdom has no choice but to ante up or fold - and a trained Battle Mage from the Guild of Arcane Combatants if nothing if not a big weapon. But what happens your generals and their generals have a common goal?
At regular intervals, a god takes control of your world's weather. Choose the gods at random each turn of the interval and begin applying their effects subtly. Their power will depend on the strength of those who worship them.
For civilised people, worship of a god actually wanes during that god's month in an effort to reduce their potential destructive effect.