daviiadams
Prince
Yes, and a good one: American migration to the west. People left the cities, to make fortunes in new territory.
That is pretty much the only way I'd have migration from big cities to others, though; Brand new territory.
Yeah, this could come into play if we had vassal states or colony options in Civ5 too, assuming there was incentive for population to migrate, depending on what social policies were in play for the home/away civ etc etc.