Civ Building is great, but that game works best in Civilization and a couple other games. The primary focus of this series is the battles, and the lead up to them. It is about the fighting and warring. Not strictly the building of the culture.

Culture, and city management are factors but they take a second seat.

As much as I love to build, I don't think it is the best focus for this particular series of games. It would mean reinventing the game, and potentially losing its essence.

There is also the number of games already focusing there and the amount of money behind them.
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Early warring states or a unique fantasy game. Perhaps a fantasy game can be spun into a movie later.....for extra dev bucks. Restore some credibility and quality to game based movies.

Oh, and detailed naval battles. Similar to the land fights in scale and visual effect.....

Please