Civil War in the Hydlaa region of the Dome (our current game world).
The Octarchy due to unforeseen circumstances flees socio-political unrest in the area, and all the factions start recruiting and fighting for control.
Some factions/guilds, such as the Warriors, will fight for peace, and would favour the return of the Octarchy to the area.
Others would seek to stop such a thing, and gain their own little patch of land.
If rp'd well, different factions would run different towns, alliances would be made and broken, and it'd be the most fun experience in a long time.
It all ends when the GMs get bored and bring back the Octarchial NPC's and rules in a sweeping reinvasion to regain control two or three weeks later.
Also, to prevent newb/merchant unhappiness, maybe the wars could take a rest for a few hours each day. Just an extra idea.