Quoting OMG_BlackHatHedgehog, reply 126I could see it possible to "win" with only one city, but it better not be a piece of cake. With NO cities at all it better be a rush strat and the game better have had finished in less than 50 turns at most.
Think Sauron or Gandalf. With a sovereign as strong as those characters you could wipe out anything. And if you add magic ... And if you don't have cities you could get a lot of xp through quests and monster killing. so when you capture your first city you could have a sovereign level 20 when your opponents have theirs level 4 or 5.
Sure... but Sauron still had an army to fight the Alliance, even though he went out there and decimated everyone.
I understand what you're saying, it should be possible to RUSH someone and win. Eg, capture their capital while their sovereign is walking around, etc. But remember that you would have no research or spell points, unless you chose those attributes when you started, or if you hired someone who provided you those benefits.
After a more economy minded individual is pulling in research and spell points and warfare like mad, you shouldn't be able to just wipe them out with your band of superheroes. Like 50 turns or so. Assuming they have a standing army.