In some of the diamonds are thunderbolts hidden, these are pretty rare. If you manage to find one, you first have to activate them by clicking on the bottom right button (the options button) that is on the right of the pop counter. To use it, you have to attack a square that is directly next to one of your squares, so you can't use ranged attacks. These thunderbolts will give you a very strong attack, which will reduce the population of  some of your enemies squares to 1. It looks like a thunderbolt hit the enemy's empire.The attack is stronger when you use more population to attack your opponent's field.