Were the zoning commissions just as restrictive then as they are today? Would the game become a bit too crazy if a province organically developed based upon their civilization, infrastructure, and population?
Allowing for increased building slots, trade routes, growth, and resource generators based upon the factors above rather than a mana power is more natural.
Allowing for increased building slots, trade routes, growth, and resource generators based upon the factors above rather than a mana power is more natural.