Grepolis is a free war strategy game just the way you want it. It is the 3rd browser game by InnoGames and unlike other similar games, the action don't take place in medieval Europe but in ancient Greece.
The world of Grepolis exist out of thousands of unique islands and each one has about 20 cities. Players need to convert one simple city into a big empire by founding or conquering other cities.
In Grepolis, there are four types of resources: wood, stone, silver coin and favor. These can be gained through lumberjack, quarry and silver mine while favor is gained by worshiping a chosen God. When you level up farms, timber camps, quarries and temples, resource production will raise.
As soon as you build barracks and academies, you will be able to build armies to farm the computer controlled villages on your island. A player should also send troops (archers, slingers, hoplites, cavalry and catapults) to the other cities to conquer them or to raid their resources.
Research in Grepolis is done inside the academy. To increase efficiency, specialization for each of your cities is needed. Roughly a quarter of your total cities should be dedicated to building Biremes and another quarter should build light ships.
Grepolis is easy to learn because there is a great tutorial that will guide you through some actions you can do.