A city builder type game. You are the leader of an ancient city state. The objective is to to make your city grow and thrive (survival / becoming stronger).
Unlike typical city builders, City States emphasizes the lack of control that real leaders dealt with as depicted in The Pelopenesian War by Thucydides, and other histories.
So you won't find yourself micro-managing an economic system, or deciding where to put the sewers, or leading the city's army in battle. As King, you have advisors, misiters, and generals to do these things for you.
So in that respect its less a city builder and more a city-state governing simulator. Perhaps "King simulator" might be a good description?
The game is still under development. All basic building types are implemented. But the game has a very deep and rich rules system which has yet to be fully implemented.