Their cavalry is weak against archers or other cavalry. With 6-8 units of cavalry, you can easily beat them at an early stage of the battle. Then, you engage their infantry with your infantry, you take 2 units of skirmishers in their back, you shoot from behind, and they should start to rout. If not, you bring your cavalry and charge them on the back. If you are quick enough, your infantry won't suffer much.