Kingdoms at War is a fantastic free strategy game that you can play free online and with the need to be able to build your city, create an empire and form your own army that will both attack and defend your kingdom, you will have to make sure your strategy is right in this one.
Whether you want to depict the aura of being a defensive kingdom or want to become one of the aggressors within the game is completely up to you, run your kingdom as you see fit but make sure that you have a backup plan in place in case your rivals attack at the same time as you do!