Empires and Allies combat is a simple and fun combat system involving a split screen combat approach with your team on the bottom half of the screen and the enemy on the top half of the screen as you kill or destroy the enemy rewards you need will fall.
When starting combat depending on the type you will have ground or battle field wars which has the two sides running toward each other with your team on the bottom half and the enemy on the top half, you mouse over the enemy troops, tank, or vehicle until it is outlined in red and then click on the enemy to fire and then collect the rewards.
There is also air and water battles which are the same as the ground battle, but instead of fighting people or tanks, you fight ships and planes. Once again mousing over the enemy clicking on them to fire until their health is zero and collect the rewards as they fall from the destroyed vehicle or troops.
All in all the system is simple, the bigger weapons you have, the better you will do in battles against other empires, the game, or invasions from other players.