Think Eve Online, get rid of the spaceships, and add cowboys, railroads, factories, slaves, and Indians.

The map would be simple enough in theory, but a remarkable achievement if actually done – use USGS satellite survey maps, and historical documents, to create a digital simulacrum of North America West of the Mississippi as it may have looked at a certain time in the 19th century.

Factions are simple enough – Northerners, Southerners, Mexicans, Canadians, and Indians.  Carve out space for your faction in the lands of the West, build up the strength and wealth of your people, and survive.  Set up farms, mines, factories, towns, etc. that are populated by NPC’s – NPC’s that you need to recruit and escort to the West, and perhaps feed, house, and support.  Cooperate with other players from various factions to do this – but be aware of which faction will gain the most from your new developments.  Engage in range wars and vigilante actions against your faction enemies when it suits you, but beware of causing too much chaos lest the army come in to settle things down.

This would be best run on instanced servers.  Each server would have a set time-dilation.  Travel and economic actions would take time in the game, similar to what they might take in the real world, but as game time moves forward far faster than in reality, things would move forward.  Allow players to have multiple characters in game, acting as part of a clan or tribe or business empire, so that they’ll usually have new orders to give and new things to do.

As time passes, the game world would change.  Towns will grow, populations will move, the economy will develop.  Along with this, political boundaries will shift.  Land may be incorporated into free states, slave states, Canadian or Mexican provinces, or it may stay under the control of the Native Americans.  These political developments would take place in part due to population triggers (so much population of one faction in an area, and stuff starts to happen), but could be molded by player activity as well.  Players could become politicans, and work for support both amongst the NPC population (by doing things that those NPC’s would like) and amongst the PC population.

As things change, the game would move closer and closer to a set end-game time, perhaps 1914.  Then, it would all start over.  The game would play out differently every single time, both due to modifications in the resources available on the map, and what sort of PC’s join the server, what faction they support, and what they choose to do.