2. A factions is much more work than a history ( in my opinion )
Making some lousy story is really easy, you are right in it. But making a really interesting story is quite hard. I haven't write anything yet (however, I have some ideas), but I used to (and still doing) critizing new stories. It's really hard to make an interesting story, especially for strategy games, since you can't use the most detailed parts (it's no use to make every unit an own personality, yet, it could make more interesting, seeing what are their intentions in a war.). Strategy's story are usually about battles/wars between 2 or more sides, yet, the intentions behind them can be deeper (conquering new lands? Maybe. Destroying other countries/religions/etc.? Maybe. Or maybe, they want to avenge a certain persons death [who was assasinated, etc.].). Also, many times it isn't clear why do people follow their leaders (they might have their own intentions, like getting money, advance into the nobility, or just using some intrigue.). And make it sound like it could really happen. This is the hardest (not because the fantasy, but making the people look not stupid [the most generic fault...].).
But if you have something interesting, I'm happy to hear
(Maybe we should ask Johndh, he has some talent it seems.)
Other:
A new faction? Once I made one that had 1 unit, and it could buy upgrades to itself (a demon giant/behemoth model), but it was quite unbalanced, since I could kill the computer every time (I thought it gets stronger if it kills more, while the other players gather more armies over time, but it didn't really succeeded...)