A chieftan could right click on the village idol or something, click "Start crusade/jihad/whatever", and then set a coordinate location on the map (cannot be in the same grid or supergrid as the chieftan's), and every other chieftan from every other village in the grid or supergrid would have the option to join in. If they do, a waypoint would be marked, and an arrow on the minimap would lead the villagers to the location.
Then some infidels and homelanders would massacre eachother.
Would this not be fun?
Oh, and the requirements for starting a crusade/jihad/whatever would be like give up a pearl necklace, and have a large village, or something along those lines.