Hero Wars and its sequel
HeroQuest (the Mongoose Publishing one), both of which focussed on Greg Stafford's fantasy world of Glorantha, did a good job with rules for communities. Though these can be used for everything from clans to companion bands, to regiments, and particularly for warbands, with the players treating them as a community to lead, defend, and draw on the resources of. The new 4th edition of the system,
QuestWorlds, which is out in February from Chaosium, also includes these community mechanics.
Some writers of Glorantha material dig even deeper into these mechanics, particularly in the Jonstown Compendium campaign book
The Company of the Dragon, which is explicitly set in a warband. These mechanics dig deep into the concept of 'the community as a character', with the warband being defined by
RuneQuest stats - STR as manpower, CON as resilience and survivability, DEX as adaptability, and so on (it also has conversion rules for
QuestWorlds). The community also has skills with ratings. Drawing on the company's resources will threaten to deplete them, so that the players will at times have to focus on tasks that strengthen or replenish resources, such as recruitment, logistics, and magic. It's a fascinating system that helps warbands come alive as entities.