One thing that separates Spartan Wars: Empire of Honor and Elite Edition (again, same game, two different names, and they are both available on the App Store as of the current moment) from other MMO strategy games is the addition of god cards. By worshipping one god, you can get various boosts for your city, such as a boost in collecting resources, speeding up training or speeding up research. By having another god lead you into battle, you can get various battle boosts. The higher the level of your god card, the more of a boost you will get, so leveling them up is imperative.
To level them up, you need to get more faith. There are a couple ways to do this. One of them is to sacrifice some of the god cards that you don’t use, but this will barely earn you any.
Another way to do so is simply to attack and to be attacked by other players. Check your attack reports, because if you plunder another player or another player plunders you, you’ll have a chance to gain faith. The higher the power of the other player relative to your power level, the more you stand to gain from the battle, no matter if you win or lose.
When you hit your upgrade ceiling with your God cards, the game will tell you that you need to level up Zeus in order to upgrade them more. You can upgrade your Zeus card if you have one, but it won’t do anything when you do.
Instead, what you need to do first is either to start an alliance or to join an alliance. Once you do this, you can go to the Statue of Zeus and worship to level him up. Your alliance will have a combined Zeus, and they will level him up by worshipping him as a group, rather than everyone having an individual Zeus.