I'd like to go ahead and mention the idea of a prologue.  I'm in this other RP on another site called [i]Rise of Domrius[/i], and in it the players are in this cobbled alliance as they try to defend a mountainpass from a Roman-esque faction.  It's really fun, and seeing the players discuss strategies is neat.

Perhaps we could do this prequel where our great houses have banded together to oust the Red Legions.  Then once that RP concludes, we start the actual RP, where our armies have returned home for some time.  Our characters would be the sons and daughters and whatnot of our characters from the prologue or something.

Or perhaps another prologue where there are two factions vying for power, and your house has to choose one.  We have this large battle between the players.  The victors choose conditions (who they want to execute, whether they take prisoners and make them slaves/wards, take their land, make them a vassal state, etc).  Then once that prologue is done, we fast-forward x amount of years and a new war is brewing.  Some of our factions may have more men due to conditions placed int he prologue, some family members of yours may belong to someone else, etc etc.

Would you guys be more interested in a single political/war RP, or do you like the idea of multiple plots?  If you like multiple plots, perhaps one can be about the warring kingdoms, one about the loyalists protecting the princess, and one can be about the senators of the Red Legion; the senators will debate courses of action against the sultanate, and perhaps one day discuss strategies to invade the western kingdoms again.