You don't need an umpire or controller to run a campaign as described, but most players would agree things go better if someone is nominated as overall umpire. The umpire can interpret the rules and improvise new ones, keep the players informed about forthcoming battles, invent special events, spread rumours, and generally keep the campaign going.
The most useful thing an umpire can do is publish a weekly campaign newsletter which summarises the battles fought over the previous week, mocks the defeated, and lists the players and the amount of territory they now control. The newsletter can also be used to announce local events and new discoveries.
For example, you might announce the discovery of a stone circle, ruined tower, shipwreck or some other interesting place. The umpire invents some suitable rules for the territory that make it well worth having. Players who want to investigate are invited to submit their names to the umpire who then draws the players into random pairs, pairing off winners until a single victor emerges. The ultimate winner receives the special territory as a bonus, and becomes the only player to possess this unique and valuable territory.
An umpire can also ensure that players don't deliberately avoid fighting enemies they fear will beat them, and he can impose penalties on players who fail to show up for battles. Perhaps he can remove territories to represent the enemy's unopposed rampaging and pillaging!
The umpire can also draw the campaign to a close once the players start to lose interest or one player gains ascendancy. A good way of doing this is to wait for two players to win a predetermined number of territories (12 is recommended) and then have them play a game to decide the campaign winner.
Finally, bear in mind the campaign is not supposed to be wholly fair Or perfectly balanced... It isn't, nor is it supposed to be! The wayward political element of allies and random acquisitions of territory will inevitably favour one side Or other. Undoubtedly the initial restrictions will penalise some armies more than others. Ultimately this doesn't matter too much, as a good campaign umpire will be able to even things out without displaying blatant favouritism!