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Even if it takes a hundred attempts, the main thing is that these factions have a clear history and ideology and are not just a collection of mindless units. And of course, there needs to be balance, but they can't seem to get it right even with only eight factions.
Take Warcraft II, for example, where the wars between Orcs and Humans differ only in appearance, but the different magic of the mages throws off the balance!
You can only make the balance as good as possible!