'You can't just run around killing goblins and looting temples, this isn't the old days my boy. To make it today you've got to be part of the guild, and you need a team, and a look, and most importantly you need a manager. Like me.'
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.