I've just got done listening to an episode of Blogs on Tape. Specifically episode 172 - Pleasures of the OSR: Emergent Story and Open Worlds, by Ben. L. This got the cogs turning in my brain thinking about "faction play" or "domain play". In particular I felt inspired to take a trip down the rabbit hole to explore what the original Dungeons & Dragons rule pamphlets says about these concepts. From memory, not much considering this original system was marketed as a "top-down" war game. However I have a suspicion that much can be extrapolated from what these pamphlets do say. So let's take a look...

OD&D Domain & Faction Play

In Men & Magic the character section provides details of high level character play, which is very applicable to domains or factions. In particular what income is available to high level characters:

"Top-level fighters (Lords and above) who build castles are considered “Barons,” [...]. Base income for a Baron is a tax rate of 10 Gold Pieces/inhabitant of the barony/game year (Men & Magic)."

"Clerics with castles of their own will have control of a territory similar to the “Barony” of fighters, and they will receive “tithes” equal to 20 Gold Pieces/Inhabitant/year (Men & Magic)." Further Underworld & Wilderness Adventures expands on this: "Within each territory there will be from 2–8 villages of from 100–400 inhabitants each. This populace will bring in annual tax revenue equal to 10 Gold Pieces each. "

Additionally, the supplements give us some more information to nuance sub-classes:

"A paladin’s stronghold cannot be above 200,000 gold pieces in total cost, and no more than 200 men can be retained to guard it. Paladins normally prefer to dwell with lawful princes or patriarchs, but circumstances may prevent this. They will associate only with lawful characters (Greyhawk)."

Some sub-classes such as assassins and monks can become grand masters or guild masters and most classes can obtain followers of some description to form part of their faction.

For fun let's take the fictional settlement of Threshold, which exists in the Mystara or "Known World" campaign setting. Not an OD&D setting, but this setting did begin as an OD&D campaign before becoming the official setting of the BECMI rules. Threshold is ruled by a high level cleric named Sherlane Halaran. Sherlane is a 14th Level Cleric and therefore a Patriarch. He does have a castle of his own; the Tarnkeep, which controls Threshold. So, according to OD&D rules the baron will receive tithes equal to 20 G.P./Inhabitant/year. It's important to remember that this is just castle inhabitants, which currently I do not know of. However another look at Underworld & Wilderness Adventures does yield an answer. Regarding castles it says "The inhabitants of these strongholds are determined at random." and if the occupant is a patriarch then the following applies:

Die  Inhabitant

1    1-20 Heroes
2    1-6 Superheroes
3    1-10 Treants
4    1-8 Hippogriffs*

* With a like number of heroes riding these creatures.

There's more. Strongholds also have guards. Underworld & Wilderness Adventures says that "In addition to those men or monsters accompanying castle residents, there will be a number of men aiding in defence. From 30 to 180 men will man the walls, one-half of whom will be crossbow armed light foot, and the balance will be heavy foot. Those castle residents who are accompanied by men or creatures capable of riding or able to make near equal speed will be mounted on horseback, as will their men be mounted. There is also a chance that there will be others in the castle’s party [...]" The book then goes on to provide a table, of which I will produce the entry for clerics:

50% chance of 1-6 assistants of level 4-7.

Threshold itself has a population of 5,000 so (5,000 * 10 = 100,000 G.P.) he receives an income of 100,000 G.P/year. Further, Threshold will have 2-8 outlying villages and Sherlane has a daughter: Aleena Halaran who is a 12th level Cleric. She does not have a castle of her own, however but is still clearly part of Sherlane's faction/domain.

Men & Magic also tells us in regards to clerics with strongholds or castles that "[...] "faithful" men will come to such a castle, being fanatically loyal, and they will serve at no cost. There will be from 10-60 heavy cavalry, 10-60 horsed crossbowmen ("Turcopole"-type), and 30-180 heavy foot. Some simple dice rolling can finalise these numbers.

Thus we may end up with the following details regarding the domain of Threshold:

Ruler: Patriarch Sherlane Halaran
Territory Population: 5,000
Stronghold Inhabitants
   Followers:   16 Heroes
                30 heavy cavalry
                40 horsed crossbowmen
                110 Heavy Foot
      Guards:   55 Light Foot Crossbowmen
                55 Heavy Foot
Income: Tax:    100,000 G.P./year
        Tithes: 6,120 G.P./year

Note that Sherlane has no assistants residing in his stronghold. This is because the 50% chance was not fruitful.

So what happens if a party of adventurers come to Threshold? We can answer that easy by referring again the section in Underworld & Wilderness Adventures on castles:

"Clerics will require passers by to give a tithe (10%) of all their money and jewels. If there is no payment possible the Cleric will send the adventurers on some form of Lawful or Chaotic task, under Quest. Generally Evil High Priests will simply attempt to slay Lawful or Neutral passers by who fail to pay their tithes."

So if you want to play an emergent game that takes into account methods of play involving factions or domains. Simply work out details of a particular place and it's power groups and follow the rules in OD&D that dictate what a party has to do when they come into contact with a stronghold. Because the play is emergent it lends itself very well to solo play. You just need a simple way of randomly generating quests. There's actually a great table on quests and geases in the Judges Guild Ready Reference Sheets that would work perfectly!