It is more for the bronze age period : a strategic map of the area cut in 1-10km² squares and you can have a big town with palace and temples on one square and resources specific villages in the squares around (and you manage the trade route on the strategic map). Because realistically speaking resource are not all on the same 10km² map.
Hence severals player cities is not only for war but also for trade and strategic goods (it is not that absurd 
)
If you play the Anno Serie there is a good comparaison to make : sometime you have to colonize an small island far from your territory because it is the only place where you can find a specific resource. It add extra depth to the game because you have to hold a thought spot and maintain the connnection (and not only an easy place with a lot of farming/hunting aera). Like I said in this post : Bronze Age Expansion - #33 by louis.mervoyer it is a bit like simcity4 regional map (which is a great city builder by the way)
However I am well aware it is CPU hungry…
…
But as time go on cities become more and linked together so something have to be made.