Coalition

i can remember when i was playing the first game and at one point, a race would get the upper hand and expand into a weaker race, then making them the largest faction. At that point i always thought to my self, i beter some how stop them before they get stronger and go after me.
My first thought was always make an alliance with someone (which was fair enough but was limited). so what i always thought was a good idear was if you could make a coalition with other factions and there soul perpose was to go after that one faction.
so the way i thought this could always work was, you could invite mulitple factions to this coalistion at once and its main funtion was just to go after that one leading faction (also this could be inversed, if you were the strongest faction then smaller ones would unit against you).
Not being the owner of any of the betas (being from scotland, and thinking shipping the game would cost me to much) im not sure if there is a system already like this already or something beter, but if there is not i would like some feedback (i know its third beta and not likly this would be implemented if it was even aproved off but just incase some form of expansion pack was released)