It looks like you are totally alone in defending this small fort. Forget about controlling armies, you must handle this situation alone with your bow. The enemies are coming.
They approach from two sides and you have to shoot them as soon as you can. This means aiming and estimating the right angle. Bows and arrows can be bought for money you get with various bonuses. The experience is useful as well when defeating dinosaurs, minotaurs or some flying stuff. However, the camera zooms out anytime you aim and shoot, that’s very annoying.